It looks as if it's been grafted to make a standard and the graft is failing.

Agree. It looks like you've lost about half the top of the tree. It looks high grafted dwarf Korean lilac. You could cut the green side back hard and hope for the best, but I think it's outlived it's useful life.

Thank you both! That‘s not what I was hoping to hear, but it makes sense after googling it. If I attempted to save it and cut the green back hard - should I also cut back the dead side? And does it matter when I do it (wait until after it blooms or now)? Thanks again!!!!

Yes. The dead side is of no use to the tree. Cut it off. Since it's dead it doesn't matter when you do it.

lets be realistic ... this is the front door of your castle ... not really a place for a 5 year regeneration project .. imo ... its time for it to go ...

if it were out back on my 5 acres.. it would be interesting to prune it up.. and see what happens .. but not out the front door ... crikey ...

i think of these kind of foo foo trees ... as short lived.. and you already got 30 years out of this one ... i think you won that equation ..

if you want idea on the future without the tree ... start a new post with a pic of the whole front of the house.. as well as big city location.. etc .. and we would be glad to brainstorm it for you ...

ken

btw: last pic.. just above.. when these types of foo foo grafted trees sprout aggressively from the bottom.. thats usually a good indication.. the top is in trouble ...

double btw: .... if you want to plant another decorative tree.. i suggest you come out to the front of that bed .. as this one was within inches of being to close to the house ...