You argue from a false premise about breaching contract/tos.
Not a lawyer either, but where does it say, that the content has to be available for infinity? There is no talk about any guarantee that said content will always be available or will never change / update / downgrade / be removed.
Especially the downgrade/change. I have seen it happen. A developer unhappy with the project totally shape changing it to something else. Or removing it. The tos does not even require a warning period or notification to download it, before it's gone/changed.
I know why I was asking which tos/law would be broken. My answer is: none! If you have a different answer, please cite the relevant law or tos section.
Consequences like risking to be responsible for refunds, damaging your own reputation as a developer, the reputation of the site you are migrating to, or damaging trust in a store's ability to provide cloud services are a different matter.