these things happen terra, my mom was diagnosed with breast cancer last October and we've been dealing with it ever since. The best thing to do is just be strong for him, maybe visit if necessary. Simba's father is gonna need that support, I can tell you from personal experience. If you do visit, attend some chemotherapy sessions, the moral support will do wonders for the patient.
It's a long recovery process, but again, simba's father needs all of the support he can get right now.