The wood underneath the peeling bark is dead. And it has been dead for a long time.

Nothing you can do about past damage such as that.

You might consider calling a certified arborist for an on-site evaluation to determine if the tree may topple or if it is stable.

Oh, goodness. What would cause it to die?

It might not die and you may help it to heal. Take all lose bark away. Then brush and wash the wood because usually there is some mugus already dedeloped depending the state of rotting. You may find some sort of animals too. Carefully see that there are no holes where rainwater and debris collects. These you have to cut open.

Treating naked wood divides opinions but I have done it. After couple sunny days when the wood is dry brush open areas with wood treatment which has rotting preventives. They are thin like water and soak well.

I need to disagree with the previous post. That info is out-of-date.

Removing the bark and/or brushing the tree and/or sealing it won't do anything to help. In fact, sealers can make things worse by increasing the moisture within the wood so that rot can readily extend.

If any "animals" are present, it's likely they are insects that live in/on dead wood. They may or may not be the cause of the dead wood.

If any holes exist, with or without water, it's not important. Water-filled holes don't rot because the water inhibits the process. But if you cut/drill a pathway for the water to drain, you will assist the existing rot to extend into new wood.

Better to have a certified arborist examine the tree and its surroundings to look for the real cause.

The dead wood has been there for a long time. It may or may not be extending any further. The tree's outcome will depend upon why the wood died long ago.

Under loose bark there is fine place for many kind of livin things to live, eat, breed and poop. It is perfectly normal in nature and unfortunately pollution we human produce has killed a lot of them. But many of us want to control process in our gardens.

On fifth picture bare wood is already grey and soon there are black spots. Sure sign of destruction. Maple wood is hard but it rots easily. I dont know the name of product but I am sure you find it at HW store. It is used on wood before painting if someone wants to build wooden houses which lasts. It is used on decks but it is not oil. It does not make a layer like paint and it penetrates in to the wood.

I am certain that holes which collect water speeds destruction because standing water is exellent atmosphere for life. Also many trees grow where water freezes. If temperature fluctuates around 32F happens the same phenomen which brokes waterhoses and brings rocks up from the earth.