if you quit, the download will attempt to restart when you start up again, and a pro install doesn't normally affect your preferences and incomplete downloads.

Still, you may lose your place in queues, and sounds like there aren't many sources for your file, so perhaps you're better just waiting (especially if the host is just a weekend file-sharer).

If you do decide to take a moment (it only takes 5 minutes) to install Pro, all should resume as before and you probably won't notice much difference. Your download might even be faster, since Pro tries to find more sources. Just repeat the search again once your Pro has connected.