I developed and was diagnosed with dermographism approx. 20 years ago. I also have chronic urticaria (hives lasting longer than 6 weeks - mine have lasted most of my life), and dermographism is often seen with that. The worst of my dermographism settled down 6-8 years ago, but it has never completely gone away. If I am having a bad day with my other health problems, it tends to be more pronounced.
But most days I just get a little red from rubbing/scratching, rather than great big welts.
I was part of the largest online support group for hivers for many years, working with thousands of people who have chronic hives, including many with dermographism.
I can tell you that many people do go into remission, I've seen it happen many times, and it doesn't have to take years and years. Some go into remission in a few months, some a few years, although some do suffer for several years.... Urticaria is a very individualized disease, and everyone is different. Unfortunately no one can tell you with any certainty when or if your dermographism will go away. But the odds are in your favor....
I have been on most antihistamines that have been on the market, including Atarax (hydroxyzine) and Allegra. Atarax always works great for me, although leaves me sleepy. Allegra is garbage, does not work at all for me. (Same with Claritin.)
I have been on antihistamines every day for 20 years, and often prescribed at doses much higher than used to treat allergies - that's normal protocol for treating chronic hives. I have not suffered any ill effects from being on them, other than dry mouth (Biotene makes a lot of great products to help counter that).
Overall antihistamines are safe for the long term, according to all my doctors and the research I've done, since I too had the same concerns at first.
My only concern would be taking any newer antihistamines, since there have been problems in the past with some that eventually had to be pulled from the US market - notably Seldane and Hismanil. I prefer to stick with the older antihistamines for that reason....