What's wrong with Hydrapack? Is this some rumor you heard or first hand experience? Not sure what kind of reservoir you're talking about, but my Hydrapack I use for mountain biking has a plastic clip you slide over the top of the entire thing. I don't see how that is ever going to pop loose. I have taken many falls on my mountain bike which are arguably harder hits than snowboarding falls and I haven't had any issues. I think it is a fantastic pack and prefer it over the numerous Camelback packs I have used.
Watch the video here:
He tests all the main reservoirs from each brand. (The Camelbak Antidote is in a separate video because the initial test as a prototype.)