No, it's going to keep lifting until it gets too heavy to hold and break off and most likely sink... not float. Of course that's due to Technic plate shifting, not due to rain.
But it'll be interesting to see if that happens first, or if the Yellow Stone Super Volcano will explode (it's already a bit over due now, but it's plus or minus is like 1,000 or 2,000 years... so it might not happen for a long while still.