>>96231964 (OP)Skill issue, OP.
Always have a plan B when any player not making it could stop the season from running.
Sometimes you can just find a reason why their character shows up later or why they're incapacitated for a session. Doesn't even need to be anything fancy. Sometimes you just get the shits.
But even if that's not possible, a good alternative is to have some world building one shots prepared. Is there anything about your world, or whatever is going on, that you'd like the players to know? Instead of giving them an infodump at some point, give them premade characters and run them through a flashback of a dramatic point in history.