You do not specify where do you live but yes, they will loose their leaves as you suspect so, they will look dead during the summer months. They loose their leaves in late November - December in the D/FW Area, a little later south of us. Then they leaf out in March or April.

The spent flowers will remain attached to the end of the stems for winter interest.

If your planned location for the shrubs provides shade, it sounds like you may prefer something like a camellia sasanqua that blooms in the Fall (they usually start blooming in the Fall; exactly when varies: some sasanquas start blooming in September while others as late as Nov) or a camellia japonica, which usually blooms later (exactly when varies but some start in November and other as late as March-April). They are evergreen. Sasanquas prefer afternoon shade but they can be planted in sunny areas too as I noticed them last year in pots by a restaurant that I frequent here; japonicas must have afternoon shade starting around 12pm or so.

Amongst all the hydrangeas, Oakleaf hydrangeas will sometimes retain the leaves thru mild winters or if in protected locations. This year was not exactly mild for me but, I have one Ruby Slippers that lost all the leaves in the north side of the house and in an unprotected location. But a Pee Wee in a protected location kept the leaves this year and just finished leafing out.