I currently have 2 players and my son in college that can play during breaks, like the last 3 weeks. At times when he is home for one week, we might play a 1-shot with a lower level group associated with the main group. When we play the main group- the PC just shows up like he was there all along.
I think we used to create a way to bring the PC into the game, but that might part of the night, so now we just "poof" him into the game. There is no worry about magic or realism or HP damage compared to the others.
There is enough NPCs and henchmen that we could make the player play with one of them but why bother?