Oh god yes, some people do give warning and if they do, I'm more lenient (and it's happened in a small group with people who've been with me for a good while). But if they end up vanishing for good or say neglect this and post elsewhere, I pretty much ask them to leave/kick em out. It's rude to me and the other players who have to pick up someone's slack if they don't post or make an effort to have good content. I have very little patience for writers who complain about having nothing to do when it's their job to meet people/plots halfway. If you like writing and the people you're with, you tend to make an evident effort and if life gets in the way, you say something. 

if you don't (and aren't happy), you're probably already giving up or life really is important you need to step down and exit properly. 

/ramble