Absolute is the only one I know of that will boot you after the 1st level of inactivity. However, once they did it to me, and I WAS there, but folded every hand, as I got nothing but crap cards. But once you play that one hand, you're good for the duration.
I've had it happen (OFTEN at Carbon, where you have 2 hours before the tourney to sign up), that is was me alone or me & one other guy. Even getting a good, fair player (no all-ins), it was a pain because 1) you cannot sit out a few hands, cuz your blinds will eb quickly stolen, or he'll steal blinds that YOU should be stealing , and 2) as the blinds to up, you're barely keeping even, while stacks at other tables are growing.
Honestly, it's not been a problem at FT. Never had more than 3 or 4 sitting out the whole game, usually just 1 or 2. Sometimes, I like to sit out the early donkfest, or am pretty tight about the hands I'll play until some of the donks are gone, or I can at least make note of who's betting what. But wouldn't be opposed to booting folk after 2 levels of inactivity, so 20 minutes.