Maybe google could make a thing where they give users an pixel for less in exchange for their old iphone (newer -> more price reduction)

With a 30 day guarantee to give the phone back (data purge and stuff only happens after) the user is not going to really risk anything

But it could be interpreted as weak, but if a bunch of users stays they can really use it as good publicity so maybe the move would not be that bad.

I am sure that google could loose a lot of money this way but they are one of the largest companies so they could afford it.