Hedge dying?

Novice here. We have a tall hedge running along one side of our back garden (see pics). The hedge separates the garden from a municipal park. When we moved here some years ago, the hedge was pretty well-established and lush. However, over the past few years, it has lost much of its foliage and some large gaps have begun to appear (our fault - we neglected it). It's also coming under assault from a fair amount of ivy. And there's quite a bit of play in the stems - some of them are very flimsy and breaking up and look like they could be pulled from the ground with ease.

The widening gaps mean that people using the park next to us can see through to our garden. Is the hedge beyond restoring? Should we rip it out and start again (which wouldn't be ideal given there would be nothing much screening our garden from the park until another hedge was properly established). Is there something else we could do to improve the existing hedge?

(The pics are taken from the park side of the hedge.)

Any advice appreciated.