I've got a few leaves that haven't wilted under water, but I suspect there is enough of the plant above the water's surface... and they'll die sooner or later, if I don't get them above the water... 25 years ago, when I did my 1st Potho's in a tank ( it was accidental back then )... I had a vine growing in the dirt, that laid over a tank, & got in the water's surface... the vine started rooting like crazy, & the vine growing past that part that dipped into the tank, was twice the size, than the part between the pot & the tank...