Sans is definitely going to go into the lab. His plan isn't tearing up the place so much as it's laser-focused on finding and getting people out, though. (Papyrus is his first priority, then Sayori, then the others, but ideally all of them.) He'll go in on his own if he has to, and his infiltration will be aiming more for quick and quiet and with minimal having to deal with doppelgangers and traps. But if people want to go with him he's cool with that, as long as they're not going to deliberately try to attract attention.

Sans does actually have familiarity with lab settings in general, so that might help with navigation? We'll see.