Special Note: Please note that this scenario is meant to be read as entertainment, not as an accurate prediction of the future. Also note that the viewpoints and opinions that may come across in this scenario are not necessarily the viewpoints and opinions of the author.
Nanomolecular disease would quickly become a life-threatening but preventable disease after cancer becomes completely curable in 2025 due to nanotechnology. Polio will make a global comeback in the late 2030s but will become extinct by 2049. Terrorists and rebel armies will attack despotic countries with polio bullets once cancer becomes nearly extinct.
The disease would occurs when nanobots exceed their half-life of 75 years; causing them to be more suspectible to malware and electronic viruses. These electronic viruses are the same kind of viruses that infect tablet computers, laptops, desktop computers and gaming devices.
Preventing nanomolecular disease is as simple as going to the doctor every six months and getting new firmware and nanobots for your body and mind. Universal healthcare makes this free but must people neglect to update their nanobots because of other concerns (like lack of time or lack of available transportation). Mass transportation will become affordable to everyone but mass transit has tendency to be crowded at times. If a typical bus is more than 60% full, chances are that a person from out-of-town would take either take a cab (taxi), use their own vehicle instead, or rely on maglev trains instead.
It will be proven that nanobots can only last 150 years in the body of the average North American male; they will completely deteriorate after that (causing the body to rapidly age). Once the body rapidly ages, the person will perish within 24 hours of the last nanobot being disintegrated into the body system. Nanobots (as well as nanoparticles) slowly degrade over time like other man-made things and it would be best to have them replaced every six months like a child's artificial limb.