Well I'm pretty sure I won't be feeling any peace or anything at all when I'm dead, so I can't argue with that logic.
If I were ever to announce my farewell on here, I would simply ask for some luck in ending my life as quickly as possible, successfully.
Still, it's better than "sending my prayers". I shiver at the thought of that being said when I'm gone. Not here, but elsewhere, amongst my religious family and their friends.
The community would have to come up with something better to say without being seen as encouraging, if you want to get rid of the "wish you peace" banality, might you also want to suggest an alternative..?