So you have a dropped section in the slab for the shower floor. *Good.

My thought, too.

IME, there would be no need for a membrane. *A layer of mortar - a rather
friable layer, heavy on sand, light on cement - is added on top of the slab
to give the necessary slope and the tile is layed on it. *Seems to me you
should be able to remove the floor tile with minimal damage. *If there is
damage to the mortar bed, just fill in with thinset when re-tiling. *

You mean to remove the tile from the mortar and leave the existing
mortar and sand base?

Water getting through the tile to the mortar bed and slab should present no
problems, the slab gets wet anyway from rain. *Just like the rest of the
slab and footers *

Sounds logical. Thanks!

Both our showers are built like that, no problems whatsoever. *No need even
for shower doors as the higher bathroom floor is also tile over the slab.

Still putting shower doors, as much water as they deflect back into
the shower I don't want to add a drain in the bathroom floor :O)

THANKS!