According to the restriction page, you will lose the ability to wear purple gear unless you purchase that ability and a whole selection of other things that you already have.
My worry is that things will get deleted between me dropping subscription and paying cartel coins to unlock what I want.
F2P doesn't mean End of the World you know:-) What happens to your characters when you drop your sub in ANY game? Nothing. You can't play with them anymore until you sub again. So why do you fear Bioware would do anything as stupid as to delete gear??