I concur with pretty much all the info above.
Planning and feeling normal are critical, so if your wife wants to plan travel, go for it. Buy travel insurance, plan away, and just see what happens.

The issue with the surgery, as you may have picked up, is whether she is going to do reconstruction. The mastectomy is not nearly as hard on your body as a cesarean (if she had one of those). I was back home playing on the floor with my kid within two days of the mastectomy. Reconstruction on the other hand, wow. Serious surgery. Drains. Expanders. I would not have wanted to travel. Even driving was uncomfortable.

So, while YMMV, I was only overnight for a mastectomy with 16 lymph nodes removed, traveled during chemo, taught summer school during radiation, traveled the day after radiation ended, and took care of two kids under three while doing 6 months of chemo and 6 weeks of radiation.

However, those reconstructive surgeries. That's a completely different matter. These are the most painful and hardest to recover from things I've had done.