The answer to the first one is yes - It’s in the other thread I think that @wewerewerewolvesonce pointed out threads left for a certain amount of time can be auto-deleted.
The problem is if we decide some threads are worth keeping (again, big discussion).
And yes, hotlinking isn’t good so Discourse doesn’t do it as standard. I’m not sure you can stop that. You can possibly force stuff to appear at hyperlinks though (maybe that’s what you mean) rather than previewing.