My endless summer hydrangeas look like they are dying. The pots didn’t have drainage holes so soil was always wet. Put holes in now for drainage. Will they come back?

I’m glad you switched to a container with good drainage. Have you read our container hydrangea guide? There are numerous suggestions to help gardeners grow healthy hydrangeas in pots. With one that is near death, I would find a spot with morning sun and afternoon shade to help reduce the stress. And, water only when needed. It might be once a day during hot, dry spells. And, less frequently, when the weather is milder. Hopefully, the roots will be happier in the new container and you will soon see new growth.