In my opinion, positive feedback should not be removed.
If you left a positive feedback, then you were happy with the deal you made and/or the item you received. The other guy not leaving feedback does not change that.
Removing positive feedback is the same as leaving a retaliatory negative feedback. Again, just my opinion.
In my experience, 95% of the time, people leave feedback, and 99% of the other 5% will after you message them.
I have had two members not leave me feedback. I let the first one go until this thread started or it may have been another version of this thread. Anyway I PM'd both members and left a friendly reminder. Both left me feedback shortly after. I figure I only got 20 so I need all I can get if I am ever going to catch up with BIKER13 LOL