Normally I would expect the game to still run, even if slowly and at a horrible framerate.
That is indeed what you would normally expect from most games. When the game first loads I believe it loads a lot of the assets upfront. It takes a while when you first load it but it means when actually loading and starting a match it is very quick. Perhaps in the initial game loading it really is just programmed to expect 8gig and doesn't function without it?
Or it is possibly a bug. There is meant to be a patch out today so perhaps try again after that. If it still doesn't work then, then you can either wait to see if a dev answers this thread (with bug thread they are quite good at appearing) or get a refund.
Apart from having the latest drivers installed you may wish to check your systems virtual memory/paging file is a decent size as I read making it larger/OS controlled fixed a problem for some other people who either had "no paging file" selected or only had a tiny one. It may be particularly important with your lower RAM level. You can put it to system managed or look up the best size for your system. (a quick google search suggests it should be 1.5 times larger than your system memory. so that would be at least 9gig for you)
