Jericho is slated to remain with the company full-time through the first week of June. He will tour Great Britain with his band Fozzy the week of 6/6 and handle hosting duties for The Metal Hammer Golden Gods Awards in London on 6/11.
Jericho is slated to return to WWE the following week and is expected to work for WWE through August, at which point his band Fozzy will join The Rockstar Uproar Tour, which runs from 8/15 through 9/30.
So, if the company wants him, Jericho will be available for their June and July PPVs. Summerslam is out of the question.
Jericho is currently being advertised for the WWE European tour in the Fall as well.
So, while he is leaving and taking time off for Fozzy, he's not "leaving" in the sense that he's departing from the company forever.