The monetary policy should be fixed and unchanging. That’s what gives people confidence that the money is sound.
In my opinion, the emission curve is an inseparable part of the issuance contract. If the emission curve can be changed, so can the supply cap.
I think changing the supply cap is an unrealistic scenario. In that case it would be 15 years from now and the protocol would hard fork, which would be potentially good for ERG holders if the networks can sustain themselves independently.
Just like holding bitcoin before bitcoin cash, you would get an equal amount of tokens from both networks of the hard fork.