It does make sense, in fact it's the only way it makes sense. The events of the original trilogy should remain unchanged because they would be the outcome of DOFP. Spideyboy is pretty much right on the mark.
But yea it would have to create a whole new dimension/timeline where the OT doesn't even exist, which also is kind of a bummer, you don't want to undo the previous films.
As I've said before though, there's never real logic when dealing with time travel, the paradox will always be there. You can't explain the first 2 terminator movies, hell even the first one, without them undoing themselves over and over. It's an endless loop. Anything that happens in DOFP should technically lead to the OT as we have seen it.
You just have to hope the filmakers entertain you enough, and to not make glaring problems even bigger with time travel. It has to be glossed over somehow in a way that doesn't make you think TOO deeply about it, but still be smart entertainment. Such as t1and t2. They make zero sense, but you wouldn't know that watching it really, unless your mind was in another place not being entertained.