Wait a bit longer - the damage to various JMs around here went from a few injured leaves to complete defoliation, depending on the tree and the location. Some have begun to grow new leaves and some are still sitting there. As long as the cambium - the layer right under the bark - is still green when you scratch lightly on a twig, the tree is alive. You may have some tip die-back to trim off, but the tree itself should be fine. Most trees have auxilliary buds; they will grow and leaf out soon. Wait until the leaves are clearly growing before you do any trimming, and be careful of the emerging leaves. Resist the temptation to clean off the old leaves, unless you did it straight away - you might damage the emerging buds. Water the tree well, but don't drown it, as JMs don't like standing in water. And don't fertilize until the tree has almost all the leaves out, and then lightly with a slow release fertilizer.

Japanese maples are prone to a number of die-back type diseases, some more serious than others. Several are very weather related and even those that are not tied directly to weather may be indirectly tied - out of season or extreme weather conditons can stress the trees which makes them more vulnerable to these pathogens. So last year's drought, hurricane-type winds and heavy rains, late freezes, etc. could all create a stressful environment and increased sensitivty. Pruning out dead wood is always appropriate and may be helpful as well. Be sure to clean/sterilize pruners well. Keep adequately watered this summer and as necessary later. By next spring you should know whether this tree is worth keeping.

Not old age. Japanese maples can live for many decades with the correct care and no disease issues. Yes, it could be something serious. JM's are extremely prone to certain soil pathogens that can kill a tree very rapidly, almost overnight during the growing season, but can also work its slower but equally fatal way over the dormant season. Knowing where you are located might help in sussing this out. The summer drought(s) experienced in many part of the country last year could have overly stressed the tree and a stressed JM is even more prone to these disease issues. If confirmed as dead, taking a branch sample into your extension office for diagnosis is advised, as at least one of these soil pathogens, if present, would preclude planting with another maple (or any other susceptible species) in that location. So it is best to know exactly what you are dealing with before making other planting choices. And very difficult to determine accurately outside of a plant path lab

Not sure there is a lot you can do for it at this point. JM's are prone to a variety of soil pathogens that can severely damage or even kill the tree. This one looks like it might be dying a slow death :-(( What I would suggest is getting rid of all the rocks - they are not helping and could be hurting the tree. And carefully prune out all the dead wood you see. It will be a pale color, often gray, compared to the dark color of healthy tissue. Dead wood tends to harbor insects and allows an inroad for other disease issues. Then just keep the tree adequately watered - not too much, not too little. Just don't allow the soil to dry completely. And no fertilizer!! If the tree does not respond or seems to get worse, then it's time to contemplate removal. But I would be cautious about replanting with another JM until you can confirm what caused the problem (and that may involve a path lab analysis), as some of these soil pathogens will infect any other susceptible species planted that space. Going forward, you might want to post any other questions you have about Japanese maples on the Maples forum. This one is pretty much inactive and most JM enthusiasts post there.