Specifically whether or not there is a mass value which would be a modestly stable liquid? I'd say "probably", but answering that question definitively would i

Specifically whether or not there is a mass value which would be a modestly stable liquid? I'd say "probably", but answering that question definitively would involve breaking out some fancy planetary modelling techniques and looking at the phase diagram of water. Make it too small and it'll sublimate away like a comet, as you say. Make it too large (ie approaching Neptune mass) and the core will be in some non-liquid phase (either an solid or a non-molecular plasma type phase). I'd guesstimate there to be a decent range of values in between, though. Smaller than Earth with a thick non-water atmosphere? Might work.