Yeah the death sentence would make for much deeper RP.
Theoretical situation*
Some guy gets drunk and shoots a fellow survivor, almost killing him. We lock the shooter up until we can think of what to do with him. Some say he should be killed because he's too dangerous and he'll only hurt the group if we let him live. Others say that it's not our right to kill him, and we should just permanently take alcohol away from him.
It's not like the discussion would last more than a few minutes, so the imprisoned person wouldn't just be sitting there, and we could let him talk too. I think it would make the RP deeper, and more realistic... I don't see any down side to it.
Also, if you don't want to have to sit in jail, don't do stupid things. I know that, for example, being drunk is RPing, but your character should recognize that it's too dangerous, and he could hurt someone. Otherwise you are a threat to the other survivors, and you should be dealt with.
Than let people deal with it. It's always dealt with. Sometimes people are kicked out. Sometimes they are escorted to another area and kept on watch. Then the "prisoner" can attempt to escape - and if he does escape, he isn't going to hang around the survivor base for obvious reasons. Your idea is too forced, players already can and will do this on their own.
You're just subtracting from the freedom of the role-play. You want people to actually be locked in with no escape, just because of their character. That could get boring very quick, and they would most likely leave. If they don't leave, said player will decide they don't want that to happen again - so their character will have a sudden change in personality, which is very unrealistic, considering realism is what you're aiming for.
All in all, this is already possible. Players can already do this, and it has been done before. I should know, I was tied up with some spare rope before and interrogated before my friend foolishly let me go to the bathroom alone and untie my hands - whereas I untied my feet, knocked him out and ran away to the Wild Territory. This role-play is controlled by the players. If they want to, they will take someone to another location and keep an eye on them. It's just that most players recently like to deal with things upfront and not delay it. We don't need to actually lock them in a building.