Every time Castiel had died in battle or protecting the Winchesters, he hadn’t minded. In fact, he’d been fine with it. It had been honourable, his life for the lives of his friends. He couldn’t imagine a death he’d welcome more.
But having his vessel dragged into that water, taking him with him, he was furious. He fought it all the way, the Leviathan winning with every step. His death was being used, all that could come from it was the spread of evil and he imagined that had his vessel been able to cope, they would have stayed inside him, not caring that there was an Angel trapped in there with them. He thought about that as they dragged him under, knowing that in some abstract way he had to welcome this death too.