In my view, they pretty much mean the same, yes. But in the last one (although we obviously can understand both the meaning and the context) to disappear in two weeks may regard a vanishing in two weeks right after the speech or right after the moment when the sentence might be eventually spoken. On the other hand, to disappear and give up after two weeks turns more clear that the vanishing will occur after two weeks of study, specifically. Only saying in two weeks may sound ambiguous since it can be referred, as I said, to two weeks starting from now (the moment of the speech). Anyways, it might be an exaggerated analysis since both of them can, for sure, communicate definitely the same information.