Aiptasia, only needs one cell to rejuvenate I heard. Also when you go to bother it. It will go into protection mode (when it recedes into the live rock) and repopulate mode. So if you get a peppermint shrimp (that actually wants to eat it, because once they find a better food source. You they will stick to that), aiptasia eating file fish, or copper band butterfly bothering it. I would be afraid the aiptasia would go into reproduce or grow back from the cells left attached to the live rock in their hidey hole.
I have tried the hot water method. Didn't work.
A lot of the treatments for them has to deal with that paste in their mouth. Seen a video when it is done. They kind of implode. Once again. What happens to the cells that are still attached. Lemon juice works I heard also. Inject it in the mouth with a hypodermic needle. Just be careful with the lemon juice. It will spike the pH.
Glad you caught it. Keep it out of the DT till you 100% know it is gone.