I came with a 4 year limited plan, parts and labor not included - I regret that now cause there is a part or two that I really would love to have updated. Back in the day, if someone would have been around to say "Hi, I'm Jamie with McKinney Dodge", then I probably would have been talked into purchasing 13 or 14 maintenance plans. Some of you get that, some of you don't. I'm not the best at keeping my oil changed on a regular basis and I currently have pretty high mileage. I think the old timers call it "rode hard and put up wet". My tires aren't quite as bald as others and my joints tend to squeek occasionally. I'm more like a GMC Gremlin in a world of Cadilacs. If you're too young to know what a Gremlin is, then that should be info enough - however, here is a Gremlin:
But to be serious, if you're talking about maintaining fitness, you really can't maintain a high level of fitness without having to continuously re-build. You can keep fit and keep a lot of fitness, but you can't maintain what you would call your "peak" level of fitness. You can keep building and revisiting that level though. Usually after I have peaked for a particular race, I drop back and start over at an appropriate point and base that on what my next "peak" is geared towards. I've heard it told that you cannot peak more than once a year, and might be able to squeeze out a second peak maximum. I find truth in that. Also, there needs to be some constant changing and adaptations to maintain, there has to be periodization, and there has to be a lot of rest built in.
Periodization, like Eric said is the key. I stick to aerobic, sub-threshold rides. FWIW, my maintenance plan is not working because my FTP on the bike is down 20% from 2 years ago and my 5k times are worse than last year.
Jamie does have a plan for the off season. But to "get your money out of it" so to speak, I would focus on something you'd like to make stronger and focus on that during the off season. I wouldn't do swimming, I'd pick running or biking. Have Jamie design some plans geared towards what you have in mind - faster and stronger on the bike, or running speed, etc. Still work on the other disciplines that you aren't focusing on, and maybe even drop the swimming to once a week. Just some ideas.