Better to have cut it to the ground in early spring, but done is done...., if it is well established (in the ground 3 years or more) and if you water it as it needs it, it should sprout back just fine. You MAY have to do some judicious thinning to keep it from being a crowded mass, if all goes well.

It is about 15 years old and I cut it down better than 2 weeks ago.

I will have to gave it a good watering tomorrow. I am hoping it does come back.

I transplanted a 3-4 year old one last fall and cut it back to about a half-foot. It was fine this year, albeit very small. Not the same timing as yours, but I think it still indicates its a tough plant.