I agree that no back and forth is possible between Vegas and Ibiza during the summer.
However, June, Jully and August don't scares me because not much appens during those months in Vegas (the weather is too hot, 45 degree Celcius everyday). Big months in Vegas are April, May and September (I don't care about May or April, cause the season is not started yet in Ibiza).
What is scary for Ibiza, I think, is Septembre (Vegas could outpaid Ibiza like it appened with David Guetta). That would be a shame to see Solomun and other DJs leaving the Island late August...