Concrete porches pulling away from home and cracking
No, you cannot repair them. If a large concrete structure is falling apart, it means the foundation is not good. Putting a deck over it to hide the disaster is probably a good idea. Obviously, you should make footings below the frost line for your deck, unless you want the same thing to happen to it.

Personally I would probably build the deck and then sell the house and try to distract potential buyers as much as possible.