Really fun video. Getting a consistent group together is probably the hardest part of running a game. If you can enjoy a game with even as few as one or two players, that can work well.
I use a few tricks to keep groups going:
Have six full-time players.
Have two "on call" players – these are players who are interested but might not be able to commit regularly and are willing to jump in when a spot is open.
Run with as few as four. This means it takes five people cancelling before you can't run a game.
Run at a consistent time each week.
Run shorter games – I go for 3 hours.
That's helped me keep multiple groups going for ten years with one group consistent for about 20 years.
You don't even need to have someone else running their character. Just say that the character is busy/drunk/sick whatever match their role-play. Or simply have an agreement with the PC that despite being unrealistic for the sake of the game, nobody will wonder why a character can be absent in the middle of space or a dungeon without any justification.
I understand that in game with a big focus on party balance/tactic it may-be different but this kind of the game is the exception not hte norm
The problem only happens when a group feels they need to delay if someone can't make it. As a GM I have a set day/time and play without the missing players.
If there are three players present I'll run. Unless there is something big upcoming, then we'll discuss if we want to postpone. I usually say "I want four players, so I'll recruit to five, and run with three".
We had a regular schedule and multiple games with different runners. If the scheduled runner could not make it and no other runner was available or ready to run then we played board games that many folks in the group always had available. Runners would also decide if they want to go with missing players usually getting feedback from who came as part of it. So then it came down to how much people were ok with putting it off. Granted said group would sometimes have someone buy a new boxed game and we would just play it because folks wanted to.