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Immature hydrangea leaves often have a purplish cast. Also, it is possible that it is caused by a lack of nutrients. Have the soil tested. It may be a phosphorous deficiency. Purple leaves/foliage are often a sign for this deficiency. Regardless, adding a little phosphorous will not hurt the plant. In fact, it may even help with getting your shrub to bloom. Here is more information: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/phosphorus-plant-growth.htm

This sounds like Chlorosis. This article will help with that:
https://www.gardeningknowhow.com/plant-problems/environmental/leaf-chlorosis-and-iron.htm

This article will help: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm

It there any pattern to the die back (new stems, older stems, etc) and are there any other signs of disease? This will help us better determine the type of problem.

I would also go ahead and inspect the roots and look for burrows in teh ground around them. You may have a rodent problem and they may be chewing on the roots of the plants.

This article will help you:
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm

It doesn't look good for your hydrangeas. Either they dried out too much during storage, or they got too much sun and burned. You can try planting them in the ground and hope for the best. Next time, try giving your winter stored plants a light watering once a month. Sorry the news isn't better.