To the latter questions: yes (or roll for an adventuring NPC if there's one in the party); and maybe yes if it's certain my character will be dead or otherwise out of action for some time and there's no way to get a replacement in.
For something like that long Abyss adventure used as the example just upthread, were I the DM I'd drop some loud hints that they might want to bring two characters each on this trip because in-the-field replacement won't be possible should anyone die or otherwise become unplayable. I'd also try to ensure there's at least one adventuring NPC in the group as a second fallback.
It wasn't a long adventure. Or, well, there wasn't much left. It was just that I got hit immediately after we got to the important part of The Abyss at the start of the session, which was actually supposed to be close to the very end of the adventure. We had already killed just about everything. And we couldn't heal it because the cleric player was absent for a few weeks. Ostensibly, that was okay; we had a magic item that someone else could use... a staff of life that anybody good aligned could use. Which by this point meant... the cleric or myself the paladin. Unfortunately, the staff was command word activated. You start to see the problem. I also had a holy mace of my deity that let me cast greater restoration once a week (among other things). But, again, it was command word activated. Oh, sweet ironies.
The other part of the issue was that... I think it started to just frustrate the DM. He made the whole dungeon after killing the boss a puzzle, and I was the only one that figured it out. We spent two sessions wandering around the demon web pits finding clue after clue, and random encounter after random encounter, and none of the other four players that were there figured out what was going on. I passed a note to the DM (I mean I was bored) that indicated I knew exactly what the issue was, exactly what we needed to do, and exactly which room we needed to do it in. But the other players decided they needed to withdraw and rest or try to find a way out, which they couldn't. I think the thing we needed to destroy was also dimensionally locking the whole complex. That's why we needed a MacGuffin to get there. So it was just going to get progressively more frustrating and TPK the party. Nobody was having fun anymore.
At the end of the second session, the DM said, "OK, while you guys are hiding out trying to rest, and the paladin's holy artifact mace breaks his Feeblemind," basically. He dressed it up, but that's what happened. We beat the adventure the next session.
Honestly, the DM just expected me not to fail the save, and maybe forgot that those things were command word activated. I still have that character saved on my Google Drive because it was such a good campaign. At 15th level as a single class human paladin I had a +15 Will save before any buffs, and Feeblemind was a 5th level spell then so from the trap that I triggered it was only DC 17. I literally had to roll a 1 to fail. My character had famously survived Disintegrate traps perhaps... two dozen times? Every time there was a trap that we missed, somehow I always managed to trigger it. It became a running joke that it was always Disintegrate magic. Part of the reason I was so good looking was because I exfoliated regularly!
If I had it to do again, I would just tell the other players what was going on. The fact that my character was out of commission shouldn't remove me as a player from collaborative play. Several other characters in the party had high Int. They should be able to figure it out even if me as a player with no character is the one doing it. But few D&D players think the game plays like that, and even fewer thought like that ~20 years ago. Still, I have no doubt that most people that only play D&D even today would not like that.
That turned into a sort of bittersweet ending for a very, very long campaign. About 5 years spanning AD&D and the migration to 3e. Shortly after, I ended up taking a job and moved across the country for a few years like a month later. I've since moved back and play with mostly the same group, though. So definitely a happy ending really.