Maintenance is important in the off-season, but it is also very important you participate in a variety of activities that stress you in different ways. If you plan to get serious for next year my first word of advice is to join a triathlon club, if you can. They are cheap, effective for training motivation, and socially fun. The next thing you should do is plan a weekly schedule. If you don't schedule it, you likely won't do it.
Training has to be regular to see positive gains.
For exercise, do it daily, with a mandatory one day off per week rest. Let's get something straight here. I don't expect any of you to give up everything to train for triathlon. What I'm encouraging is an active lifestyle. There are many things you do already which fit into this lifestyle and into a triathlon training program whether it be a basketball practice, a mountain bike ride, or a long hike with the dog.