> If we get effective humanoid robots

That's still an if and also a when; could be 2 decades from now or more till this reliably replaces a nurse.

> Retraining to what exactly?

I wish I had a good solution for all of us and you raise good points , even if you retrain to become say a therapist or a personal trainer the economy could become too broken and fragmented for you to be able to making a living. Governments that can will have to step in.