Hi - I have a shower drain that has failed. The waterproofing failed and the yellow tongue substrate below the tiling rotted out to the point that someone could put their weight on the drain and broke it around the flange. The remainder of the flange has been removed and you can see from the attached photo that the substrate on top of the joist has rotted due to the failed waterproofing.
We're planning on doing some building work at the house in 12-24 months so looking for a short term fix that will make it operable but doesn't involve a fully bathroom renno. The room is tiled floor to ceiling and the tiles are way out of production, so it seems that any option involving cutting the floor out won't be possible as the tiles around the show would all need to be replaced to allow contiguous waterproofing to be applied to the floor and wall?

The only option I can think of would be to remove the frameless shower screens and place either an acrylic stand-alone or tile-over shower base over the existing tiling (something like this), seal this against the walls and then place the frameless screens on top of the new shower base. Any major issues with that? I know that's far from optimal, but really looking for something that would be functional and last a couple of years. What would be best to use to bond the shower base to the existing tiles?
Thanks.