If I were concerned about licensing, then I'm really not sure I'd put my faith into a library like this - not least that if the app just shipped with the dll, then it could be swapped out in the blink of an eye with a stub.
There's significantly more involved in managing this sort of thing that a simplistic library such as this can manage.
Companies concerned with licensing usually do it because they're protecting their assets from software piracy. Something like this would be horribly easy to circumnavigate.
You're using a simple pseudo random number generator as well (as opposed to a cryptographic one), which is incredibly weak, and, as others have made clear, making a direct DB connection is an absolute no-no: Your methodology of requiring a directly connecting to a remote database server, that is also required to be accessible 100% of the time, is critical point of failure.
I can't imagine anyone (outside of the really big name vendors) that'll have customers that'll be "forgiving" enough to be blocked simply because there's an issue with the remote database.
Not used them myself, but something like https://licensespring.com/ seems to provide significantly better license management.