If you are on a relatively low dose, do not crave more, etc,
you are not likely to crash.

Since you have used this for 6 yrs with success, and do not feel a depressive crash later in the day, then you probably are okay with it.

Focalin is methylphenidate-- and like other stimulants (amphetamines) changes the dopamine use in the brain.
There have been reports that high dose, long term use of stimulants may create depression later down the road. But your experience seems pretty stable and you claim you don't need increasing doses. Should you stop taking it, you may feel depressed or not depending on your own biochemistry and neurotransmitter status.

There has also been the warning that long term high dose stimulants may lead to Parkinson's in some people. But that hasn't been proven either.
Here is a study to this effect:
http://www.ncbi.nlm.nih.gov/pubmed/19587858
In essence is that while you are on this drug, you may avoid PD if the future holds that for you. Discontinue however, and that may change. Long term studies on children just have not been done or if they have are not released by the drug companies making methylphenidate. So we are sort of in the dark about this topic, still after 50 yrs of this drug being on the market.

Here is another article in that vein:
http://www.ncbi.nlm.nih.gov/pubmed/17982908