For weight maintainence, healthy eating is definitely more important than exercise. It takes a hell of a lot more effort to burn 500 calories than to cut 500 calories from your diet. I'm no exercise nut, but I do a lot of cycling (70-75km/week this summer). I don't find it relaxing; if anything, it's the most stressful part of my day. But, it wakes me up in the mornings and forces me back into the real world at the e…
If you don't exercise, you loose muscle, replaced by fat. Even if your weight stays the same, your fat/muscle ratio will change, and you wont look good, or feel healthy.
Exercise is a must. Gym, running outside, playing co-ed sports (soccer, volleyball, whatever) are a must. If you don't at least one of them, your body will suffer.