I do some paid posting with PPP and there is a thread on the PPP forum right now about this subject. The thread has a poll and 91% of the bloggers who have responded DO NOT remove paid posts. I don't know the thread addy right now but if you want to look for it go to
http://boards.payperpost.com
Why would we? We write the posts so that they become part of our blogs with personal experiences included in the paid post. Plus, a good portion of my site traffic comes from search engine searches - a number of these searches takes people to my paid posts. I'd lose site traffic if I removed the posts.
The problem is with PPP not the bloggers. PPP can only guarantee a link for 30 days for the advertiser ... otherwise they'd have to be checking our sites on and off for a year or for all time. So they've worded the TOS in such a way as it seems that we only have to keep a paid post up for thirty days. Some bloggers take that literally, but PPP does recommend that we leave the posts up and I can tell you that the majority of us do leave the posts up.
If the bloggers are picking posting opportunities that truly suit their blogs there should be no reason to remove the posts.