Royalty + Ideology, no mods.
This seems to be an old bug, as i found multiple mentions of similar issue:
I received a quest to rescue a pawn named Сакого. She was set as quest reward.
2. What happened:
A few days later, when I went to the quest map - it turned out that the pawn rescued is
not the pawn that was originally mentined in the quest description.
And in the quest window there was no line with reward for the quest ("Сакого will join").
I loaded older save and found out that reward pawn allways disappers at specific game time.
I was expecting to find the pawn mentioned in the quest description on the quest map.
1) Load RewardPawnDisappears.rms
2) Check rescue quest "Спасение Сакого" - reward is set to Сакого
3) Wait a bit (~2 game hours)
4) You can see that at 12:00 game time - quest reward disappears
5. Savegame file https://www.swisstransfer.com/d/cf06ee0d-a955-4b88-b234-b4507677808b
I just figured out why this happened: this pawn died of hypothermia while waiting for my rescue caravan to arrive!
Thats why she was quietly removed from the quest ???
I still think this is a bug - I expect the pawn to be alive at least before I enter the quest map.