welcome to GoY

I am sorry to say that does sound as if it is dying/dead. The wood shouldn't crumble at all.does the bark come off all the way around the trunk? if yes then it is dead. Have you or another family member used a strimmer right up to it? or deer/rabbits been nibbling at it?

Now they can be contrary plants, my brother cut his off at ground level as he decided it wasn't worth the space it took up, the following spring it regrew from below the soil.

so it is worth cutting it at ground level and keeping your fingers crossed.
if it was a grafted specimen what grows may not be the same colour as the one you had.

hope this helps.