Before the Xi'an Incident, his focus seemed to have been on finishing the civil war. But what about after the civil war? Did he have a plan for retaking Manchura after the Communists were no longer a threat?
He was going to unleash his German equipped forces on the Japanese in a signature battle to draw the Western powers into this war. He was going to retake the North East of China yes.
Xian incident contributed, but he didn't immediate declare and act on the Japanese. It wasn't until Beijing was in the Japanese's crosshairs and a full on invasion was all but inevitable did he finally commit his best against the Japanese in the battle of Shanghai.
His plan since 1937 was really his plan all along. It didn't work so well, obviously, he lost almost all of his modern troops in one battle. Half of his new officers about ~10,000 were killed. He didn't expect the Western powers to be as indifferent as they were.