How much commitment do we require?

[Not Known 15]

Well, it depends.
There is always the possibility that you get ill. This is a valid excuse for having to be replaced out. And it will happen to everyone long enough on the side.
If a type of game has an unexpected post frequency, way more than normal then people might get problems(e.g. 1000 posts per day).
If you are new to mafia/to a certain type of game then you don't have the experience and can fall into a pitfall by misunderstanding how much time you need, but this should not happen more than once, ideally not at all.
The schedule of people changes sometimes in unexpected ways, but this should not happen too often.

All of this means that some, infrequent replace outs, just happen.
If people want to replace out for the wrong reasons, or replace out too often, then something should be done.