Welcome to the forum, Tim! Given your description, you are in a good position and don't need to worry.
I wonder what your symptoms are when you do drink alcohol? Obviously something made you realize that you were having symptoms, and this could provide us with a bit more info for us to offer advice.
Like you, I am highly triggered by alcohol (as are MANY mast cell people). I go into fullblown anaphylactic shock from many things, and one of them is alcohol. I knew something was not right in the beginning because whenever I had even one sip of alcohol, I would instantly start aching in every muscle of my body. It was very strange. So, that was my first clue. As you can guess, you should NEVER have even a taste of alcohol at any point in your life. The reason is that you don't want to get ill, AND you don't want to tempt your condition into progressing further.
I am a strong believer of avoidance for triggers. That is only logical that if you avoid triggers, you will stay stable and continue enjoying a happy life. Generally, I would tell someone that they need to be on the proper preventative medicines and avoid triggers. In your case, it doesn't sound as if you need any meds except as a rescue medicine to handle the symptoms if you trigger. Now, if you only trigger to alcohol, that should be easy to never need a rescue med as long as you don't drink any alcohol. If you begin triggering to other things, though, then you would want to identify as many triggers as possible, avoid them, and take daily preventative meds. It really sounds as if you are much luckier than many, though, and don't need the daily meds. The bottom line is to let how you feel be your guide.
By the way, ISM (abbreviation for your diagnosis), is not going to change your lifespan.
Just be aware and make any necessary adjustments as needed.