If I have Win 7 and not Win 10 will I be unable to play this game at all?

According to the system requirements, at least here on GOG, it runs on 7, 8 and 10 so it should be fine. If it doesn't end up working, GOG has a great refund policy so you could get your money back if something changes!

Thank you a million for the reply and the load off my mind!

No problem! :) Unfortunately, though, you'll probably need to upgrade or get a dual boot with 10 because more and more games are going the route of not supporting 7. It's really stupid, I hate that we're being punished for not wanting a garbage OS, but it's the sad reality. Thankfully, we still have great companies like Larian and even CDPR who realize that there are still a lot of people who prefer Windows 7 and they're offering support for as long as they can.