No, there are simply FAR too many variables to say. Will it last? Probably. Will it fail? There is a chance. Lot's of people have a similar setup to yours on their WRX's and don't have problems, others do. The question you are asking simply cannot be answered with full honesty. If you are simply looking for a number, 20 years.
Edit: Forgot to mention the whole "glass transmission" argument is a lie. These are essentially the same transmissions that have been used by Subaru for nearly 20 years in Japan and make equal or more power when modded. My 18G and trans have done just fine, and I can beat on it pretty good. You'll hear more of ringland failures then trans failures.