Hi DR,
I had a facial schwannoma, which was unfortunately cystic. I had it re-sected in June of 2011, and by March 2013, it had double in size and I was needing another operation to have it completely removed. I have complete paralysis of the left side of my face. If it's not growing, I would definitely encourage leaving it as long as possible. Obviously the operation is not much fun, and the permanent paralysis of your face is not great either - although obviously small in comparison to loss of life!
There are many ways that you can have the paralysed side of your face re-animated, and I can now produce a smile by biting down after I had a masseter nerve transfer. I would caution against leaving it too long, as the side effects can be downright deadly. Mine grew to a whopping 5-6cm, which was putting extreme pressure on my brainstem.
If you have no symptoms, hold off. But be careful. And if you feel any type of symptom, be sure to report it to your specialist.
Hope that helps.
Cheers,
Matt