I would require a player to restart with the regular buy in.
lets use our game as an example. Tarlo has 500 bucks at 11 pm. Takes off for an hour and comes back (would never happen, but lets pretend for discussion).
Would you let him buy in for the 80, or the 500? I think I would make it the 500. That's taking a sh%t ton of money off the table.
I'd also want a reason why a home game player is leaving for an hour. If its for the purpose of taking money off the table, then that is kind of sh%tty.