Sure, they could go find new people who do this job for free (and thanks to the API changes virtually tool-less) or hire people to do it for them. Whether those people will be equally successful in nurturing their communities, who knows.
But it's definitely an option and probably only a matter of time before it happens.
They kinda already are. The problem is finding new volunteers to cover them.
This is basically on the level of a church or homeless shelter disrespecting their volunteers. NPOs only thrive on the contributions of random people investing their efforts, and a social media platform has some parallels to the model.