Getting knocked out of it ? I don't think so. Never seen it happen either. Getting pinned or hooked out of it will happen though.
They'd be sucked right back in if they were knocked out by any sort of blast from their enemies(that is something that I saw and experienced).
Maybe combining the knock back from enemies with an escape that doesn't quite get you out of it. Like a Pharah or a Junkrat that tries to escape with a concussive or a rocket jump.