I agree with Micron re they probably could supply a key if they wanted. I recall when we purchased a software product (back in the '80s) there was a contract that said the source code was held in escrow in some 3rd party organization. Even though we had the executable (and not the source code) the bottom line was -if the supplier failed for any reason, those who were in good standing with maintenance etc - had legal access to the source code.
I would think that a key or access to some process could be made available for some modest fee. It seems the company wants to force existing/former clients to the new software and related fees.
In your case, I don't know if it's possible, but am wondering, if you installed a separate copy of the software on a separate machine and used the same password/key, could you run that copy successfully for another 25 head? I think that would be similar in concept to the company unwillingness to provide some assistance to you. That is, you make use of what you have since the company has "dropped" you. Now, this wouldn't work if you have to be online and there is some check with a verification/authorization utility to ensure only "current license terms/users" were executing the software.
Just some thoughts for consideration.