Once any file is uploaded they are always at risk.  Some sites like Deposit Photos got caught red handed continuing to sell assets even after they were deleted....well deactivated.  At DP you don't actually delete, they only deactivate. I would say that most would delete your work but not all.  The licensing also might also dictate their availability to certain customers for a period of time.  So while those clips may not be available to any customer they might be in a lightbox and remain available to that customer until that asset is purchased or removed from the lightbox.  Others who may have purchased your work might want to renew a license and you will see a sale from an already deleted clip.  The fine print of the contributor agreement for each site is your starting point. In a nutshell, most will just delete the clips.