That is a tricky call especially without knowing what the license is for (and I can understand if you don't want to say).
How much does it cost per year?
Could it make sense to keep it for another five years just in case you decide to move paths? At the five year mark, you'd be only five years from your projected retirement and it seems like the license would be even less important than now.
However, it's tricky to say whether you should keep it for five more years given that I do not know if it costs $500 or $1,000 to maintain.
And I understand it was difficult to get. I think some would say the time spent to get it is akin to a "sunk cost" and so to ignore that even though it's not easy to do so. =-)
If a similar situation helps, I'll add this. I had a business structure when I ran my own consulting business. Every year, I paid $300 to keep the LLC alive. Eventually, I did not want to work on the business. I gave my clients to others and I kept the business "alive" for a few more years. When I felt ready to close it down, I did so. That saved me the $300 in fees as well as the money I used to pay an accountant to handle the tax work.
My situation is not exactly the same, yet my decision was based on 1) whether I felt ready and 2) whether I would use the business structure.
Hope this helps!