Having studied atmospheres a bit I concur - Earth can't get so hot that it
wouldn't rain anymore. I'm not entirely sure the Earth would even be dehydrated
the same way Venus is supposed to have lost its ocean. Hydrodynamic outflow of
gases from Venus' exosphere in the early days of the Solar System was driven
partly by the much higher UV put out by the early Sun.
However a "wet Greenhouse" is hotter than a high-pressure autoclave, even if
the oceans are still around - with about 10 bars worth in the atmosphere. Could Earth be
tipped towards that end-state? We really don't know, but the end of the Cryogenian
glaciations via a massive greenhouse was the worst seen since the hot times of the
Archean - and the Earth didn't tip then. Would our little perturbation really be enough
to push the Earth's systems past that point? Maybe not, but it could end up with 50 C
temperatures in the Caribbean like during the Cretaceous...