Is it possible to go 2-3 years without a single manic depressive episode while being on no medicine?

Yes: It's possible -- but i don't know what the person's illness you're talking about, is typically like. Sometimes people discontinue their medications because they don't want to take them. If a person with bipolar illness stops medication suddenly, s/he is more likely to have repeat episodes than with a more gradual taper. Also, substance abuse and erratic sleep/wake cycles make this more likely too.

Agree with Dr Pappas: Here is the thing- people can have different periodicity of cycling. One person may cycle quickly and another may cycle more rapidly. Additionally, an individual might have lengthy "normal" periods or depressive periods with fewer and shorter manic or hypomanic episodes. So the answer is yes.