Yes, of course the civil war would have taken place regardless of what was going on. There was too much disagreement between the north and south, and too much polarization between the political parties. Not to mention, the United States still managed to fight the Lakota Sioux during the civil war.
Yes, the civil was still going to happen, because the country was still strongly divided between the north and the south. There where beginning to argue on certain topics, and there was no other option but to go to war and fight it out to decide how the country would be.
The war might have been longer, possibly, but the war would certainly not have made the states reconcile. The causes of the issues between the states were actually far deeper than anything could be fixed by a common enemy, and it would like have been a two front war for the South.
The U.S. Civil War would still have happened had the Mexican-American War of 1846-48 lasted longer. This was a short-lived war, and also only affected a few states. The northern states and most of the southern states still held their personal feelings toward those on the other side of the map. There were many issues brewing at the time, but the Civil War was inevitable.
Had the Mexican-American War lingered for longer on the general conscience, it may have reduced a desire to fight the civil war on the battlefield, and a long enough delay may have led to the abolition in slavery naturally in many State legislators, reducing the likelihood of a Southern Coalition capable of uniting agains the Union.