My guess is that someone will step up and continue to create patches for XP, because you're in a pretty big boat.
But if I were you, I'd switch to a newer OS and run the whole XP box in a VM (note you may run into some MS licensing issues setting this up). Then at least you can slowly start migrating and at least your "main" hypervisor OS will be fully patched. Doesn't help you with the firewall, though.