I always could tell when an urchin had kicked off by the spineless empty shell of it that I would find.
When I moved my abalone from one tank to another, it would sit in one spot for well past a week. I thought it was a goner but eventually sprang back to life.
Couple months back I bought another abalone, a really wee little 1.5" thing and it did the same thing, sat in a spot for weeks. Thinking that this was normal I didn't think much of it ... until I found it half eaten by the CBB. So ... I guess somehow the tankmates know a little better when something's checked out than I do. I guess what I'm getting at, if it doesn't look like the other critters are eating pieces of them then they might not yet be dead. Hopefully they come around.