I went digging through all 400 or so comments, and so far I haven't found out an answer to that one. All I've found out is that once you do the trial offer one time, it can never be done again--you just keep the extra icons. I don't know what happens if you already bought extra icons.
ETA: Oh, wait. Closest I've found is on page 12 of the dw_news post. A question by nina_nicky. They say they had 70 icons uploaded last time they bought a paid account. Those went inactive. When they activated the trial offer, 30 icons reactivated, as is correct in that case. So the other 40 wouldn't if the paid account has expired. But if they aren't expired, they probably won't.
no subject
ETA: Oh, wait. Closest I've found is on page 12 of the