isolate properties before destroying them

I hope to test this properly after getting #1082  going. 

I've notice that view accessors can return undefined during view dying. I think this might be due to accessors getting updated by other ones `unset`ting. My thought is, what if you isolated everything _first_, then killed all the properties? Then you can be sure you don't get random updates as properties die.

Hope to get perf tests to test this hunch.