"Not necessarily without ticking off the vendor and/or breaking contracts..."
That probably wouldn't matter to a company living on the "razors edge" as it was put. Besides if there were decent sums involved the chances are a savvy outfit could negotiate a licensing deal with the vendor (or current rights holder). Some income is better than none from the vendor's PoV.
It still doesn't change the fact that they were mugs to buy a bit of plant that would outlast it's irreplaceable control system by several decades...
I note that the usual trio of are downvoting a suggestion to do a bit of reverse-engineering or leverage Open Source when the vendor solution amounts to FOAD. I would hate to be one of their customers. :)