Thank you for sharing your use cases and letting us know how use this functionality. If it is indeed used widely, then we may bring it back in one of the future versions. That will depend on the number of requests we receive regarding it.
But for now, I can offer you a way to bring it back in your store. Here is a diff file that will return "Save and process payment" in the admin panel to your store. You can apply it as described in this instruction.