Is deep depression about to come or can I just stay at hypomania?

Not Sure. Some people remain at a level of hypomania or mania for long periods of time. There would be a risk of eventually having a depressive episode but there is no guarantee that it would be severe. It is important for you to seek good and consistent treatment if you have problems with your mood.
Very rare. I have never seen someone remain with hypomania. What goes up eventually comes down. The question is are your truly bipolar or do you have adhd which can look like chronic hypomania? See my chapter: confessions of a bipolar over diagnoser and seeing adhd in psychiatry in techno colors on amazon.Com.