I've never done gear and I don't really know much - so grain of salt and all. I think, as alluded to earlier in this thread, the Test - not the Deca - should be your concern, with regard to your hairline. Deca, in my limited understanding, has other drawbacks to be concerned with.
As to keeping gains, I think IIRC, Deca gains include a lot of water, so you'd lose some weight after ceasing it. You should be able to keep the majority of your gains by proper diet and PCT.
Again, I'm no where near an expert and this material is covered better in the stickies.