I am happy to hear everything is going well with your Silverlight project. We are committed to continuing supporting Silverlight for as long as our customers need it. At the same time, we see a continuous drop in its usage and I expect once the user base becomes small, it will not make sense to continue investing in this product. At this point, I am unsure whether it will be before or after the official end-of-life of the technology.
Once Microsoft ceases support for Silverlight, I doubt there will be many ways to continue using your Silverlight app. Even today, there are only a few browsers supporting it, so it is great that you guys started porting it to WPF.
If for some reason you would need to continue using your Silverlight app, our licenses are perpetual and you will be able to continue using it for as long as you need, but no further features and improvements will be added to the suite.
I hope that you find this information useful.