Particularly in biological systems we don't actually know until it happens and is well studied. organisms have complex genetics & behaviors that turns on/off and we cant totally know (heck mothers cant even predict babies making messes to prevent it), but sure some of the above likely but hardly guaranteed.  But its sort of a silly hypothetical situation that isnt plausible, much more plausible is climate linked sitution: if all ice caps melted, salinity will naturally decrease but hardly 50%, more like 1.7% more water & less concentration.   Humans could also extract salt but it'd take far longer than 3 months even if it was essentially free money (decades if lucky, centuries realistically). As for volume idk how much it would lower sea levels as claimed, seawater is denser & by removing ions the density could revert closer to 1 so volume may not change as we expect. Geology might shift too, quakes and volcanism due to mass effects.