That seems to indicate a catastrophically low bus factor--people get sick, take vacations, sleep, quit, etc. If you’re blocked on an IC doing anything other than finishing their task you've got a bigger problem than them going out of pocket for a day, fix the real problem.

(If they're a manager/decisionmaker of some sort then they better learn how to multitask online, which is like a 30 year old skill requirement at this point)