I'm playing with a large group (approx 9 people, plus myself as DM). We had a full house last time, but that's unusual.
I'm planning on running when we have at least 5 pplayers, we haven't hit that low floor yet.
Anyone that is missing, their character is "forgotten". Can't contribute, can't die. Basically like they never existed. Requires some buy-in from everyone of course, but actually less buy-in than when you have to make stuff up for the critical character that is there-but-not-there. I don't like to have players having to babysit other players' characters, and I really don't want to be doing that myself either.
Everyone always gets the same XP (milestone advancement), regardless of attendance.
I encourage (but don't dictate) the party to handle treasure thusly:
All income is pooled.
Firstly, there is a pay-out for party-critical stuff:
a reserve fund (for future Raise Deads, etc)
spell components for casters (and spell-writing for the wizards)
armour for the melee folk
healing potions, antidotes, etc
Only then is the "profit" given out for characters to spend on their own stuff. (I am open to players buying magic items, using the Sane Item Prices as a basic guide).
Magic items go to the most deserving, including anyone not there, but miscellaneous stuff goes to the folk who attended.