“They’ll have to” is a pretty strong statement assuming you don’t actually have insider information on their API spending.
For now, they do use Google Maps and I’m happy with it. If they stop and it’s no longer as useful to me, maybe I’ll stop using it.
If they become popular they'll have to move to OSM, Google's steep charging for their Maps API at high usage that has brought companies to their knees is well known [1].
[1]: https://www.hackerneue.com/item?id=35089776