It's REALLY nice that things in vis_contents glide around correctly, however if they move into a turf that doesn't have vis_contents, they just instantly disappear.

Would it be possible to have them "glide" into nothingness? rather than just vanish?

I can produce a test case if wanted.
No, unfortunately it wouldn't be possible to handle that scenario without considerable difficulty. The thing of it is, they're no longer on the turf and the visual contents system does not take neighbors or overhangers into account.
Fair enough, it's wonderful otherwise and it's only a minor annoyance.