Re: When players leave games
RL can affect any of us for a week or two. I generally have no worries over that time scale (However, I reserve the right to NPC any character who is holding up the game), but if a player hasn't logged in for three months I assume they've dropped out.
However, I don't usually remove the character or player from the game immediately. I retain the status quo until/unless it becomes a problem for me. I can NPC a character whether that character is assigned to me or still assigned to a player. It's my game and I do what works best for me.
If the player asks to be removed, I'll remove them and transfer the character to me, only deleting it if I'm sure I'll never use it again. As StarMaster says, there are always uses for a pre-generated NPC.
If the game flags on their sticky list annoy them enough, they'll contact me, otherwise they could be there for quite a while. In one game, I have characters still assigned to players who have been absent for several years. If they ever come back, I'll listen; if they ever ask to be removed, I'll oblige. Meanwhile, the character can sit on the Cast List until I have need of it, it's eating no meat.
A bigger problem for me is players who go through a 'RL period', when their posting rate drops and they're neither in the game nor out of it. Particularly if their posting rate has previously been high and their character has become quite central to the story. Something like that can be far more damaging to a game than the drop-out of a minor, replaceable character.
Not their fault, of course, RL has to come first, but it can give a GM major headaches if the helicopter the PCs are travelling in comes under fire from surface to air missiles, and then the pilot has six weeks of college exams, or their child gets sick...
NPCing a character for a minor combat, making a few dice rolls, or assuming that the character will move along with the rest of the party is simple, but when major PCs have major decisions to make that will affect the direction of the game, and they're not present, what do you do? Make the decision yourself and railroad the players? Give it to someone else (who?) Talk about the weather OOC for a few weeks? Have a 'miraculous calamity' befall the key character so that someone else has to take over? Whatever decision you make, you can be sure it'll be the wrong one...
What do the rest of you do in these situations?