If health bars are staying still and there's a warlock in the raid, I'll say "hey can I get a summon please?" Otherwise I just head over on my own.
I find it funny how many people label themselves as the "omw" folk when anyone doing raids in this game can say for sure that the majority of WoW players are not. I think a lot of people like to see themselves as the type to start heading their own their own and will conveniently remember those few times when nobody else was going.