I had my RP on July 11 2014 followed by 33 sessions of RT ending in mid March this year. I was told by the oncologist before the RT that I would be very unlikely to get a natural erection after this.
I've had success with the Muse applicator and the vacuum pump but one year exactly from the RP, I had a normal erection!! It had to be worked on to achieve it, but there it was none the less. it doesn't work every time yet, but I'm optimistic it will - so you never know!