Yes, and what I but in bold letters for this mod, not to use protected followers for Vilja but ONLY essential followers!
Hindsight is wonderful, isn't it? So easy to overlook a detail like that. And all that was needed is setessential FormID. So when you install or reinstall the mod just type help Character Name. The form ID is returned which is what is used to set the NPC essential.
Now, open your game and in the console type Save funclist 1. This creates a text file of the saved game in the saved games folder. Search through it and try to find the name of your dead NPC. Once you find it (wishful thinking, copy and paste a few lines of text above on down to a few lines below each instance of that name and post it here. We might be able to figure things out from there.
If we can associate the NPC name with a RefID then you can resurrect it.
If you have a saved game before the NPC died the funclist will definitely have it's RefID
AFAIK, some of them have been Vilja's followers during the game so far. The one in bold are the one I remember I guess have been the ones which died when they followed her. But resurrecting them has no advantage, as I explained, when I dismiss one of her current follower to add the one resurrected and dismiss the one again, the situation will not change. Still she can have only how many she has left after the others died, it is still needed to cleanup the died followers from her follower framework count.
BTW, there is a mod
www.nexusmods.com/skyrimspecialedition/mods/19250 to get more info from NPCs etc., also display the RefID ...
160319B1 290/290 0000024A 78 Jensine - Base Data(24) AI Data(20) Factions(181) NPC Skills(52)
1603197F 286/286 0000024A 78 Lyne - Base Data(24) AI Data(20) Factions(177) NPC Skills(52)
160400F9 286/286 0000024A 78 Saeliah - Base Data(24) AI Data(20) Factions(177) NPC Skills(52)
160318B6 286/286 0000024A 78 Mabrelle - Base Data(24) AI Data(20) Factions(177) NPC Skills(52)
160319AF 282/282 0000024A 78 Vienele - Base Data(24) AI Data(20) Factions(173) NPC Skills(52)
16054533 282/282 0000024A 78 Eirisse - Base Data(24) AI Data(20) Factions(173) NPC Skills(52)
160318DC 278/278 0000024A 78 Enya - Base Data(24) AI Data(20) Factions(169) NPC Skills(52)
160400F6 278/278 0000024A 78 Agna - Base Data(24) AI Data(20) Factions(169) NPC Skills(52)
16031987 278/278 0000024A 78 Liviane - Base Data(24) AI Data(20) Factions(169) NPC Skills(52)
1603189D 278/278 0000024A 78 Violet - Base Data(24) AI Data(20) Factions(169) NPC Skills(52)
160319D5 278/278 0000024A 78 Michelle - Base Data(24) AI Data(20) Factions(169) NPC Skills(52)
1603198C 274/274 0000024A 78 Weyna - Base Data(24) AI Data(20) Factions(165) NPC Skills(52)
160400F7 274/274 0000024A 78 Arnynne - Base Data(24) AI Data(20) Factions(165) NPC Skills(52)
160318C4 274/274 0000024A 78 Courtney - Base Data(24) AI Data(20) Factions(165) NPC Skills(52)
16063867 274/274 0000024A 78 Lucilla - Base Data(24) AI Data(20) Factions(165) NPC Skills(52)
160318E1 274/274 0000024A 78 Suleen - Base Data(24) AI Data(20) Factions(165) NPC Skills(52)
160319D2 274/274 0000024A 78 Lynette - Base Data(24) AI Data(20) Factions(165) NPC Skills(52)
160318AB 274/274 0000024A 78 Claire - Base Data(24) AI Data(20) Factions(165) NPC Skills(52)
160318B8 274/274 0000024A 78 Viania - Base Data(24) AI Data(20) Factions(165) NPC Skills(52)
1600C3C0 274/274 0000024A 78 Tamda - Base Data(24) AI Data(20) Factions(165) NPC Skills(52)
160319B4 270/270 0000024A 78 Vallba - Base Data(24) AI Data(20) Factions(161) NPC Skills(52)
160318E8 270/270 0000024A 78 Teretia - Base Data(24) AI Data(20) Factions(161) NPC Skills(52)
16081ECA 270/270 0000024A 78 Alessandra - Base Data(24) AI Data(20) Factions(161) NPC Skills(52)
160400F8 270/270 0000024A 78 Yanne - Base Data(24) AI Data(20) Factions(161) NPC Skills(52)
160140E0 270/270 0000024A 78 Kirginia - Base Data(24) AI Data(20) Factions(161) NPC Skills(52)
160319CD 270/270 0000024A 78 Herna - Base Data(24) AI Data(20) Factions(161) NPC Skills(52)
160318E7 264/264 0000024A 78 Miraette - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
1600C3C2 264/264 0000024A 78 Veronica - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
160140CE 264/264 0000024A 78 Eila - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
16063866 264/264 0000024A 78 Khalida - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
160318D6 264/264 0000024A 78 Samanta - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
16031913 264/264 0000024A 78 Shayla - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
160318F9 264/264 0000024A 78 Linda - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
16013606 264/264 0000024A 78 Rebecca - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
160319B2 264/264 0000024A 78 Fylenne - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
160319B3 264/264 0000024A 78 Diella - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
160318BE 264/264 0000024A 78 Tuula - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
16015BE0 264/264 0000024A 78 Maria - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
16031904 264/264 0000024A 78 Valasca - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
16013099 264/264 0000024A 78 Bella - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
160319EB 264/264 0000024A 78 Sharli - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
160318CA 264/264 0000024A 78 Elira - Base Data(24) AI Data(20) Factions(157) NPC Skills(52)
1600EFC8 260/260 0000024A 78 Rikka - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
160319DB 260/260 0000024A 78 Jada - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
160319C5 260/260 0000024A 78 Rina - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
160140DD 260/260 0000024A 78 Haru - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
1600EFCC 260/260 0000024A 78 Dafnne - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
1604A310 260/260 0000024A 78 Leibwache - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
160319FE 260/260 0000024A 78 Jane - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
1600C3C3 260/260 0000024A 78 Mery - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
16031991 260/260 0000024A 78 Sannlith - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
160319FC 260/260 0000024A 78 Arisse - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
1600C3CD 260/260 0000024A 78 Lamia - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
16063865 260/260 0000024A 78 Ivy - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
160319EE 260/260 0000024A 78 Arlina - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
160319C3 260/260 0000024A 78 Stephanie - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
16013601 260/260 0000024A 78 Lielle - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
1600C3BF 260/260 0000024A 78 Kirginne - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
16063868 260/260 0000024A 78 Joscelyn - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
16081EC8 260/260 0000024A 78 Ethelinda - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
160318EE 260/260 0000024A 78 Catarina - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
16063869 260/260 0000024A 78 Zella - Base Data(24) AI Data(20) Factions(153) NPC Skills(52)
160140D6 256/256 0000024A 78 Thraria - Base Data(24) AI Data(20) Factions(149) NPC Skills(52)
16063864 256/256 0000024A 78 Elisabetha - Base Data(24) AI Data(20) Factions(149) NPC Skills(52)
160319E6 256/256 0000024A 78 Krissa - Base Data(24) AI Data(20) Factions(149) NPC Skills(52)
160319E1 256/256 0000024A 78 Arah - Base Data(24) AI Data(20) Factions(149) NPC Skills(52)
16031995 256/256 0000024A 78 Ridene - Base Data(24) AI Data(20) Factions(149) NPC Skills(52)
160140D3 256/256 0000024A 78 Ruanne - Base Data(24) AI Data(20) Factions(149) NPC Skills(52)
160318D3 252/252 0000024A 78 Tatriana - Base Data(24) AI Data(20) Factions(145) NPC Skills(52)
1603191A 252/252 0000024A 78 Lulanne - Base Data(24) AI Data(20) Factions(145) NPC Skills(52)
1603191D 252/252 0000024A 78 Elanneh - Base Data(24) AI Data(20) Factions(145) NPC Skills(52)
16012B30 252/252 0000024A 78 Joanne - Base Data(24) AI Data(20) Factions(145) NPC Skills(52)
160140DA 252/252 0000024A 78 Kerannah - Base Data(24) AI Data(20) Factions(145) NPC Skills(52)
0001336B 236/236 0000024A 78 Mjoll die Löwin - Base Data(24) AI Data(20) Factions(129) NPC Skills(52)
0F006FF8 235/235 00000A0A 78 Nadya - Base Data(24) AI Data(20) NPC Skills(52) Face(128)
000133BB 216/216 0000024A 78 Thongvor Silberblut - Base Data(24) AI Data(20) Factions(109) NPC Skills(52)
5D000D62 212/212 0000024A 78 Selene Kate - Base Data(24) AI Data(20) Factions(105) NPC Skills(52)
0D27FC9A 208/208 0000024A 78 Darcy - Base Data(24) AI Data(20) Factions(101) NPC Skills(52)
000133BD 203/203 0000124A 78 Uraccen - Base Data(24) AI Data(20) Factions(93) NPC