Yes, ages! That many would take me hours.

Generally we don’t do something else if more than one is missing, because we’re all busy and could use the time! But I do fantasize about doing one-shots with 3 players on those days.

If 1 of our 5 players is missing, we continue, unless their character is particularly important that session. Generally the DM runs their PC in encounters (with some help from players), and the character doesn’t otherwise participate much as an NPC unless necessary.