Hiya,
I've been training and racing for 10 years now, and I can tell you that taking weeks off (because you're sick or injured) starts eating into the higher-intensity ends of your fitness first and foremost. If you took 2-3 months off, you'd not only lose most/all of your Anaerobic and Threshold-level fitness (read as: hill climbing-at-speed), but you'd start losing your basic aerobic fitness. "Use it or lose it" fully applies here. If you want to do well on a 100-mile ride, even if it's non-competitive, you need to do something during those 2-3 months to preserve at least your basic aerobic conditioning.