Too much rain? my plant is brown - can it be saved?

[as110]

I received a large plant from a friend abut 2 months ago. I don't know what kind of hydrangea it is but it is supposed to be very tall and they got rid of it because it overwhelmed the front of the house. Our backyard soil is very bad, full of clay and it doesn't drain well.
I dug a huge hole and removed the clay and the rocks, replaced it with garden soil and planted the large bush into it. It can tell it got a bit stressed from the transplant, the stems bent down to the ground but it survived. The stems turned upwards and started to bloom. We had a good few weeks of bloom, the flowers were not too large but I was happy that it was ok and hoped for next year it would grow and "overwhelm" my own backyard where I have lots of room and need large plants for privacy.
There are 2 more plants from this large one that I separated at the time we dug it up. I planted one beside the house on the front in a raised spot. This lost all the leaves soon after the transplanting and looks dead so I cut it back to the ground and see what happens. The other is smaller I planted it to the street beside a lamp post and seems to have survived the transplant however it does not bloom because it is still small. It still has green leaves and the stems are upright. I planted these 3 in different parts of the soil to make sure something would survive and I didn't know which spot was the best for them (not to have all my eggs in one basket so to speak).

Anyway, in the last few weeks we had so much rain that each times it looked like we had a flood. The top soil is eroded and washed over our land. Water in a 3 foot deep hole (where I removed a tree) is up to the top and it cannot drain. Then we get more rain and there is always water in the ground. I am almost sure the plant is suffering from too much rain because the soil is so soft I sink to my shin in the clay soil. All of a sudden the flowers turned brown last week and by now all the leaves are brown and so are the stems. There is nothing green left on this plant. The soil is still soaked. We get a bit of sun every day and more rain that just pours non stop. We never had this much rain in this area.

Can this plant be saved if I replant it into a pot? To another area? Make a bigger hole or raise the bed it is in? Is the garden soil too soft/muddy? Do I need to add rocks back into it for drainage? Any advice?
thanks in advance