I'm on a semi-low dose of testosterone, but not taking any hormones besides that. If you're on testosterone, you don't need other hormones. Though you will need your testosterone levels checked because not having to fight against as many female hormones may mean you need a lower dose. If you're not on testosterone, talk to your doctor because then you may need something. Either testosterone or estrogen will work.
It is DEFINITELY not an emergency right after the surgery though. Basically, it is an increased risk of problems like osteoporosis, loss of bone density, a long-term problem rather than an immediate one. I think there might also be an increased risk of heart disease, but again this is not going to happen overnight. Relax, get through the surgery, recover, then go talk to your doctor.