Suppose a closed-source program you use has a critical vulnerability in rustls and the company that wrote it is out of business. How much effort do you need to

Suppose a closed-source program you use has a critical vulnerability in rustls and the company that wrote it is out of business. How much effort do you need to hot-patch the binary in a safe manner? I routinely use 15-years old software which is only usable with replacing libraries with their recent counterparts and changing the names to masquerade for the old ones. And I do prefer to have access to old files.