You would NOT lose most of your gains with a dbol only cycle - you WOULD lose all the water you gained though. I don't know why you think the muscle you gain would magically fade away after the cycle was over.
But sure, a dbol only cycle is a bad idea. I would stick to test. I was considering a dbol only cycle for a while because my wife didn't want me using needles, even though she was okay with the idea of steroids in general for some reason. So anyway, I looked into it quite a bit and decided it wasn't worth the time for me. You can only go on for 6 weeks tops unless you really hate your liver. But dbol is definitely potent... but in the end, injectable test will give you better results.
You should really have "your friend" do the research himself. 8 weeks is too long, in my opinion. How old is he? bodyfat %?
Does he also realize that Test Enanthate is typically quite a bit cheaper than dbol? You can get a full 12 week cycle of Test E for half the price of a crappy, low dosage dbol cycle. And you still need all the ancilliaries with dbol, so you aren't saving any money there.