Next Sunday we'll play Cold Fens 2.5 - the second half of the delve that got cut off by time constraints in the middle of a combat.
Normally, in a situation like this, I'll do a split session. We'd finish the fight, people would return to town, and then we'd do the downtime activities and go back into the dungeon.
But this time, the fight promises to be as least as long as it's gone so far. And a player who missed last session will be there. He'll end up either running someone else's character for a bit, or wait bored while the group fights out the battle. That would be fine if people reacted to close, dangerous battles by speeding up, but they don't in my group. They react by slowing down, and carefully considering every option - this is why the partial TPK we had couple sessions back took an entire session to resolve what turned out to be the result you could have predicted hours before.
Not only that, but the trip back to town and then back to the dungeon will take some valuable play time, half of which Bjorn's player will sit through.
What I'll do instead is make an exception for this session and just let the delve continue. It'll count as one big delve for XP purposes (MVP is still per-session), but Bjorn (and anyone else) will just show up.
But he won't just show up. Oh, no. I'll do what I do for the bad guys - roll for appearance.
On Bjorn's turn, make the roll, he can move onto the map (drops down from the trapdoor, turn ends.) But what roll?
I'm debating a few different ways:
1) n in 6 - Probably 1 in 6. If it turns up n or less, he appears.
2) Flat Roll-Under - Something like a 9 or less. Roll 9 or under, he appears.
3) Escalating Roll-Under - Something like 6 or less, but then each turn, increment the roll by 1. So 6-, 7-, 8-, etc. until he makes the roll an appears.
I played a game once that had reinforcement totals - you'd roll dice and record the result, and when you got enough points you could "buy" reinforcements from your off-the-board list. So I could even do a total here. I won't, because I like the roll-under.
I'm not sure which one. I should do the odds and pick one that gives the cumulative progression of success that I like the most. But I like the idea that the players can't just plan on him showing up on the next turn, or after X turns, or whatever, and plan their actions around that. They'll have the desperate fight they've gotten themselves in to, and Bjorn will or will not show up on a given turn and move in to the fight.