Second question first, depends on if they've been there before. If not then nothing, best they can do is grope around in the dark and hope there isn't a drop off. You may decide to put in some sound clues, like rushing water off to the right and how the sound seems hollow up ahead (indicating a large area) or something like that but mostly they're just screwed.

As for animals that don't have infravision, well, bats don't and most other blind sense animals. I'd have to take a gander at a MM or an Underdark book to get more detailed but I think there'd be plenty that rely on blindsense rather than infravision.

Actually, you're talking 1st or 2nd ed. huh? It's been a while since I've looked at 2nd (much less first) so I'm not really familiar with their senses.