As said it will grow back. You won’t see it from yopur side so uneven doesn’t matter. When I moved into my house onr side of the rear garden had a 5ft wide privet hedge. I cut back the 3ft on my side to the metal fence buried in the middle. Re-gained 3ft width of garden. Now have a tidy trimmed hedge rather than the overgrown mess it was.
I gained 5ft of garden at the other side by removing a leylandi hedge (trunks my side of boundary) and putting up a fence within my boundary.
If it is the OP’s hedge it is pretty overgrown. No wonder the neighbour trimmed it. Though a bit of comms first would have helped.