I expect RWD to be discontinued for assembly-line-simplification reasons.
I think the nail in the coffin was when the AWD design had longer range than the equivalent RWD design. As we all know, range anxiety is the big issue for selling electric cars; there's no reason for Tesla to sell a model with a shorter range to appeal to a fairly small group of people.
I expect the RWD 85 to be around until the supply of RWD-specific parts starts to run out (leaving just enough for a repair supply for the service centers) at which point I expect it to be dropped.
An RWD model might be reintroduced later, but it won't be the same; it will be the AWD model minus parts, which is not what the current RWD model is. Expect it to have the smaller frunk, for example.