Define "turned off". A comparator loop persists just fine without any input, just like a piston loop.

It's non-volatile sequential access memory - which, in my opinion, is the same category a hard drive falls under.

I'm not sure that delay lines will retain data when the chucks that hold them are unloaded by the server.

Yep, they do.

Repeater delay lines used to not, but that bug was fixed.