Probably but it will take time to rebuild (several growing seasons). The plant will develop more stems from the crown at its own pace and there is no good way to force it to speed that up.

To boost growth, I have sometimes added some alfalfa, alfalfa tea or blood meal (a fertilizer nigh in nitrogen) to roses but not to hydrangeas. When you add nitrogen rich fertilizers to hydrangeas, they do not react with vigorous growth like roses do (there is some reaction but do not expect the plant to double in size & number of stems like some roses can do in one season, for example).

The nitrogen in the blood meal makes the plants go into "grow" mode. You can add it per label directions and add no more after the start of July. Too much nitrogen will keep the plant growing in the Fall when it should be dormant. And too much will produce less blooms or no blooms. So go easy.

Alfalfa does not have nitrogen like blood meal but it contains a growth regulator/stimulant called triacontanol and it may help. The thing is, compared to roses, hydrangeas do not react vigorously when given lots of nitrogen so they may do likewise with alfalfa. Stop feeding alfalfa in July 1st as well.

So, experiment to see what happens and discontinue when no longer necessary. Remember not go overboard with the blood meal or alfalfa & do not add them starting on/after July 1st. The let us know how the plants did!

Luis