First it looks like your lovely hydrangea is not dying but may have lost foliage from the heat or a vole or mole destroying roots. This good news is that the big leaf hydrangea or hydrangea macrophylla that you have is among the most easiest of plants to propagate. Just snip off a few non flowering branches about as long as a pencil. Remove the foliage from the bottom half of the cutting. Now poke the cut end into moist potting soil and keep the soil watered. In a month or so roots will form on the nodes or bumps that once held leaves. Then by next spring you can move the cutting to a location in the ground but still keep the new cutting moist as it grows more roots the first summer. I usually keep my rooted hydrangea cuttings in pots of potting soil in the shade for the first summer to make sure they are well rooted before transplanting out into the garden. Take several cuttings as only about half will actually root. Good luck and Keep growing, Marianne Binetti