The locals would have probably drawn their own borders in the aftermath of WW1 had it not been for France and Great Britain which created new borders for their own interests.Perhaps let the people of the region determine where the boundaries of states in that region will be. Ethnic divisions would suggest four states out of Iraq and Syria. A kurdish state, a sunni state (western iraq and eastern syria), a shia state and an Alawite state (western syria) would give best chance of peace and stability in the long run.
Re-drawing the map today would lead to a dangerous precedent and create numerous complications - the Kurds in Turkey would want their own state; the Sunnis, Shias, Druze and other groups in Lebanon might want the same; the Shias in Bahrain might ask for some form of autonomy, the Palestinians in Jordan might get similar ideas, etc. On top of that we have the mess in Yemen; where like in Iraq and Syria various countries are involved and are rivals.
We've been told that the Iraqi army and allies are making good progress and will eventually liberate Tikrit. The significance of a fairly large Iranian contingent, fighting alongside a Shia Iraqi army has got unnoticed by many and no doubt is not going down well with the Sunni Gulf states who, just as much as they want to see IS defeated, want to see Iran weakened. The irony is that the U S. In the past tried its best to keep Iran out of Iraq and in the 1980's Saddam often claimed (and received support for it, including from the same countries who later toppled him) that he was keeping the Arab world safe from the Iranian Shia "heretics" who wanted to spread the revolution westwards.
In theory, the Iraqi government with the help of regional and non-regional allies will roll back IS and liberate all of Iraq and the Sunnis and Shia will put aside their differences and live in peace. After Iraq is liberated, attention will then shift to Syria where the "moderates" it is hoped will defeat the "extremists" and after that will defeat Assad. Lets see how things turn out.