I can’t imagine why you or ATC would require one to continue the descent, but that was a given here. Yes, a sim scenario, for sure. It’s tricky and the usual response is to toggle the GA button which will lead to mass confusion here.
The keys are:
Cycle the FMS to the MAP, select FMS as NAV source, which will be missed as the GA mode does it automatically.
Select NAV and VS, once out of APPR to make the descent and level off at 2,000’ active.
I can see several ways to mess this up, GA being the first, being ready to hand fly with raw data will be the test.
GF