Trees, Shrubs and Conifers: Ailing JM, 0 by Weerobin

Weerobin wrote:
A prized acer palmatum Shishigashira suddenly developed some sort of wilt.
It's 15yr old at least, about 8ft tall.
Its position by my front door tells you how much I value it.
It has done fine over many years.
I just noticed yesterday that half the plant is essentially dead.
The plant branches just a couple inches up from the crown.
The larger portion (naturally) has apparently abruptly died.
On closer inspection, there is swelling/fissuring of the trunk just above the bifurcation.
I cut off the diseased portion as close to the bifurcation as I could.
But I see in the transection of the trunk still a large area of darkening.
Is the remained portion of the tree doomed?
Is there anything I can do about it?
Here are a bunch of pictures.
#1 is a shot of the whole tree.
#2 shows the lower 1/2 where the tree divides into a healthy and dead half.
#3 shows the withered dead foliage on the affected half.
#4 shows the cut off portion.
#5 shows the swelling at the bottom of the affected stem as well as the discoloration of the wood.