'Endless Summer' is touted to be an extremely cold hardy (zone 4) form of macrophylla and as such, should not need any extraordinary winter protection in your zone. Since I live in a much milder climate, I can't speak from personal experience with winter hardiness so you may want to offer some basic winterizing care. Deadheading just below the blossoms is fine but I'd avoid any further pruning until next spring until you can determine how much winter dieback has occurred. FWIW, ES blooms on both old and new wood, so even if you did experience considerable winter dieback, it should not overly affect next season's flowering ability.

Look for Hayseedman's great thread on this forum on overwintering hydrangeas for basic winter care or check out hydrangeashydrangeas.com for info.

I also live in Michigan (Grand Rapids area). I bought Endless Summer in '05. Only blew leaves on it from the yard last fall and it bloomed like a champ this year. Didn't cut anything.