Here is the first map I`ll show you, basically just to show you how complicated the conflict is, and how many different players are involved, including rebels, loyalists, the Syrian army, and Kurdish forces.
But the situation keeps changing. In the above map for example, Isis controlled only small pockets of territory in the north (see the black circles). But now they have extended their influence and territory as you can see below in this map:
As you can see, ISIS has taken over a much larger territorial area of eastern and northeastern Syria, and crossed into Iraq where it controls a great deal of the north and northwest of the country (and actually continues to expand both westward towards Jordan, and east towards Baghdad). ISIS is now being considered a very serious threat to regional and even global stability, with its brutal violence that frightens even Al Qaeda (who would have ever though that was possible!).
This next map from Business Insider shows "Syraq" - the virtual irrelevance of the national borders of Iraq and Syria due to the new reality of ISIS which straddles the border and wishes to create a new Islamic Caliphate controlling international territory.
Not only ISIS but also Kurdish controlled territory crosses the border, further deligitimizing the Syria-Iraq border. It`s somewhat doubtful that Syria and Iraq in their entirety will become a single new country, it is very likely that the current borders will not endure and that new states will arise in territory controlled by various parties. This is arguably already on the verge of happening in the Kurdish north. And with ISIS so well-funded, this may soon be the case in ISIS-controlled territory as well.