First thing the determine is was the shower used after the brake and did water get down onto the sub floor and cause damage to the floor.
If the floor is tight and you are not interested in a "Restoration Grade" repair you could form up a patch for the corner. To patch it I would cast a mold of the other corner and use it to lay up a fiberglass patch that can then be fitted into place. Then overlay 6 oz. fiberglass over the complete pan to give you a complete new surface. Once the fiberglass has set you would start applying filler coats of resin to the fiberglass. It will take about 5 or 6 coats to get a smooth finish and you can add your chose of color to these coats as you fill the fiberglass.
This is not as hard as it seams. Check out this site for basic instructions for working with Fiberglass. Instruction 10, 11, and 12 will give you an idea of how its done.
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Ideally it would be best if you could remove the drain before fiberglassing but that is not necessary if you mask the drain well while working.