I have a Japanese Acer which I've had for 3 years. Every year around March/April it has regrown its leaves. This year it has not. I noticed last year that the pot that it was in was waterlogged. I regretfully didn't do anything about it and left it, thinking that it would be fine. The pot was probably waterlogged for quite a few weeks. I have now sorted out the pot, but still no sign of leaf growth. Have I killed it?
It may have got root rot and died - scrape back a little of the bark covering on the stems using your fingernail to see if the wood beneath is still live. If it is, it will look greenish and maybe moist - if its dead, it will either snap off or look brown and dry inside. Check low down on the branches, near the base, if the upper ones are all dead, and if they're all dry inside, then the plant has died.