Agree with pretty much everything you said. It's the devil you know vs. creating a whole new devil you don't know.
I wonder if it's viable for OP's company to buy the company they depend on for this software, and then staff it up and get the bugs fixed. That way they retain the domain knowledge from this company, and they get everything they want done to be prioritized. This would also likely prevent any future competition if they own the company that's making this one-of-a-kind software.
I wonder if it's viable for OP's company to buy the company they depend on for this software, and then staff it up and get the bugs fixed. That way they retain the domain knowledge from this company, and they get everything they want done to be prioritized. This would also likely prevent any future competition if they own the company that's making this one-of-a-kind software.