If people are breaking CC just leave it. No point.

Pre 50 I'd say sleep but warn your tank but you've gotta remember that if you're busting out cures like mad while a mob is asleep it's gonna turn on you straight away. If I see a slept mob and the healer is getting close to stealing hate I'll be comboing that and you can cast repose as much as you like but I won't stop till I'm comfortable with aggro.

Majority of times you'll find it's the DPS that usually break sleep. But remember again a WAR can only fire off a few flashes before he's got to overpower. So maybe wait till he's done that a few times before sleeping?