A lot of posters here are going on as if Italian intervention is going to decisively pull down France in 1914. But that seems a little... presumptuous. Sure, an Italian invasion will tie up French troops, but how many? The Italian army's combat record in World war one inspires little confidence, and it doesn't take a whole lot to stop an assault through the Alps. In the meantime, is it enough to allow the germans into Paris? Hard to say, but my gut says no. France must have had troops positioned along the border anyways (Italy was, after all, a Central Power), and it probably wouldn't take too much diversion to hold that line. In the meantime, the german logistics were very strained, and are going to run out on the brink of Paris anyways.
For that matter, somebody raised the question of whether germany even heads west in this scenario or not. Its a good question that I think we really need to sort out. I suppose it depends on the timing of the Italian DOW. If it is before the Germans attack, then they strike west because, well, Italy can help in that (broad) theatre. If not, well, east may look a bit more tempting.