This would be interesting, I think suggested before. Anyway, the way I think would be best is:
The tent is deleted after 4 weeks, then up to 1 week after that, a player would have the option of finding a semi-special encounter called "You encounter: An abandoned tent".
So, after 4 weeks, it loses world-map viewing to owner, but anyone could still encounter it (rare chance, but more common than Bunker because the majority of tents abandoned would be noobs' tents).
After a total of 5 weeks, the server would finally delete the tent.
Maybe tent location would be moved, so the tent-holder can't simple walk back and take everything
I havent understood that part. What do you mean?
I think he means that, for example, if you put a tent 1 North of NCR, it wouldn't be able to be encountered exactly at 1 North of NCR after it disappears to owner, so that if the owner logs back on, he couldn't just trace it. The location would become random, or at least the same general area.
Though, chances are the person that hadn't been online for 4 weeks isn't going to be on for the 5th week (if it only stays for one week. It can't stay forever or that would defeat the whole purpose of the feature that saves server space).