I paid my money to Steam for a particular product, if they want to revoke it, they can refund my money.
If Steam is legally required to do that, their contracts with developers will inevitably have the same clauses about refunds if you disable the product.
Steam also gave you a clear notice that there was additional third party DRM on the product before you licensed it. They are also not the ones who are shutting it down.
If Steam is legally required to do that, their contracts with developers will inevitably have the same clauses about refunds if you disable the product.