Depends. 

I wouldn't [i]like[/i] it if someone took over or recreated one of my RP's without permission, but I wouldn't put effort in getting it shut down either. Honestly, I'd be surprised if someone unable to come up with their own concept to keep a game alive for more than a couple weeks, if that at all. It's good flattery (because let's be honest here, what is imitation?), but no competition. 

If I would have to leave for a very large window of time, I'd allow my players to take over my RP. It's their game too, after all.