You really have to try to get killed by microwaves, at least from radiation. If you mess with high power waveguides you could receive a burn or shock injury.
There was a case of GE technicians in Alaska working on the FPS-49 who were near the feed horn for over an hour and had their livers destroyed. That was a very painful way to die. The injury was due to thermal effects. The body does not have internal heat sensors, the FPS-49 is relatively long wave, L-band and it cooked their livers before they knew happened. That is why we have have “lock out, tag out” these days.
How did your friend ever get a lethal dose of microwaves?
I'll take an educated guess at it. The Ray-Dome {sp} of a carrier could do it most likely. I worked on the ships cooling systems for the electronics systems. There was some nasty RF hazards on the mast including ships radar.
To check the Ray Dome I had to get an Electrocics Tech to go up with me and he had to make certain it was secured first. If someone was working in the mast an announcement went out over the ship every 15 minutes "The Mast is secure while men are working aloft".