I've used peroxide before, not for aptasia, but for fighting bryopsis. Never have left the zoa's in the tank for 10 minutes, but it almost seems like it gives the zoanthids a chemical burn on the skin.
All of the ones I have dipped seem to have healed up, but i've never left them in the dip 50/50 dip longer than 5 minutes. (as a side note, the bryopsis kept coming back) maybe I should try the 10 minute dip.
The only zoanthid head i've lost has been when one of the heads didn't close up correctly, it did that thing where they try and close up, but they end up looking extra open. The dip just destryoed that head.