If you buy Fences 4 individual license, you will also have lifetime license for that version. But, if Fences go up a version, for example Fences V5. Than, to use it, you will need to purchase a new license for that version. Your Fences V4 license should still work for your Fences V4 install.
Also, it similar, if you purchase under Object Desktop now, your license will still be able to activate your Fences V4 forever. Once your subscription expire you still can activate it, what you don't have is a link to download the latest version come out after your sub expiry date. So it is strongly advice to save all your installer somewhere while your subscription still valid.
Stardock Community Assistant