The parallel port is built into one of the support chips for the CPU and as such may or may not be repairable depending on what chip it is, whether it is socketed or soldered down and, if the latter, whether you can get a repair done locally.
You can add a PCI parallel port card and tell Windows and Mach3 to use it instead.
How did you determine the port is not working? Is it all port pins or just one or two? If the latter, it might be that a reconfiguration can still make it useable.
Before addressing the repair, you need to consider carefully what went wrong and what you can do to avoid it happening again. This is why an opto-isolated break-out board is a crucial part of any install IMHO.