I once had a group project during a masters course where one guy disappeared halfway through the semester. Didn’t respond to phone, email, anything. The rest of us were discussing how to let the professor know after he had been over a month MIA (we didn’t need him but didn’t want him to get the group grade) when the professor emailed us to say he had heard from the guy, who had been literally hit by a truck and was still in hospital; medical withdrawal.