We also had the fitting break on our 2001 Adventurer. The water heater was in a miserable place to remove, so I decided to fix it in place. I had to remove the pump and move some of the tubing to get at the back of the water heater. When there was access to the rear side I used a 1/2" easy out in the broken fitting and removed it. I replaced it with a brass fitting because that's what I had. It might not have been the best choice since the tank is aluminum, but it worked fine another 6 years and 70,000 miles before we traded it off.
If you do have to remove the heater, and it has the "motoraid" option be sure to disconnect and plug off the hoses to the engine before you attempt to remove it. Check carefully when you disconnect the hoses. Some models have an access plate that can be removed to gain access to the fittings.
Unfortunately our 2001 Adventurer 32V was one of the models that didn't have an access panel. That was one of the main reasons I decided to replace the fitting without attempting to remove the heater. Another reason was the caulking they use around the front panel of the heater. It holds exceptionally well and is miserable to remove. It takes a heat gun to get the caulking warm enough for it to release without damaging the panel.