They'll see each other again. So long as they're alive, they'll see each other again. That's how I choose to interpret the line, "Because if you die, I won't get to see you again."
As someone who works in suicide prevention, the nature of my work is that I will often never know if someone's going to be "okay" or not in the long run. I speak to them for an extremely short period of time, get them through the roughest hours, and I never talk to them again.
I, and many of my colleagues, choose to believe that our "clients" will be fine, eventually. It's a belief that stems from practical necessity. Because the alternative, living with that much unresolved closure, can be crushing. But it also stems from faith in the human condition.
Mio-san will be okay. I choose to believe it.