So, you had to choose between the code that was still Open Source and the code that was now proprietary.
If you stick with the Open Source, what you describe does not happen.
If you moved to the proprietary, well, there you are. You clearly decided that the new features were more important than it being Open Source.
Remember, it is only the new features. All the old code remains as open as it ever was.
The original code remains available under the original.
Any proprietary code would have to be code that was added on top of that.
You always have the ability to keep using the Own Source code. That is a freedom you have.
If you decide that proprietary version is “better” and choose to use that, well that is a freedom you have. But now you have accepted a proprietary license. Your choice.