if tiles are ready to come off due to long term exposure to water the idea of chipping off tile is the frustrating way to go ....what are you saving??? the 1/2' or 5/8" drywall? Why?
I have remodeled tub tiles...even sectionally taking it down to the studs and trying to match the old surface plane with the new...big hassle.
Now if tile is to removed I just remove tile so that my sawsall can slice the wall off in large hunks...underneath there is now time to evaluate the plumbing if only insulating the lines. The only matching line you have is at the top of the tile which is forgiving. The smoothing of old mastic to create a flat plane on which to mount new tile is difficult and imperfect..leaving an uneven new tile surface.
To me it is a waste of time to chip & smooth. The dust factor is the same, the injury from tile shard factor is reduced by removing the wall, upgrading the wall with insulation....new small heater fans in the bath...new vent fans near the toilet...insulated hot water pipes...NICE PACKAGE of function. To only retile is like a new paint job without the preparation work.