One does not simply dissolve poison. It'll spread very fast if he moves often. Withdrawing slows the poison's effects, and he might eventually hit him with a well-aimed Ice Beam (breaking the ghost's concentration), but by the time that happens, the damage will have been done, and the Wortortle will go down if he hasn't already.
If the Ice Beam does hit and he misses and goes down, he'll be easily dispatched by the Golbat, who would otherwise be on an endless playing field with the ghost, if he didn't disappear.
If the Wortortle lands his hit again and the ghost goes down, then Shellder will handily finish him off, and the Golbat will be under pretty extreme pressure to bring down a healthy Shellder that's already in a position to strike.
If the Ice Beam does hit and he misses and goes down, he'll be easily dispatched by the Golbat, who would otherwise be on an endless playing field with the ghost, if he didn't disappear.
If the Wortortle lands his hit again and the ghost goes down, then Shellder will handily finish him off, and the Golbat will be under pretty extreme pressure to bring down a healthy Shellder that's already in a position to strike.