Water it, remove it from its present pot, put it in a much bigger pot (volume x 3) with dry new free-draining soil (30% coarse sand, 70% slightly acidic soil/loam), don't water it for a few days, and I think it should recover.
So far, it's not a "bonsai" if it has ever been, but once it has recovered it will become a nice plant that will remind you of your grandfather.
When it's healthy again, you can take cuttings (these root pretty easily) : the "offsprings" will be the best tribute to his memory, they can travel and please, and even delight new people.
If it dies, buy another one, and remember him.
I know how you feel: I offered a Crassula ovata to my late father some 20 years ago. My mother kept it for years...
5 years ago, it was about 80 cm tall and wide in a 50 cm wide/deep pot. It flowered every winter in the lounge.
It was on the balcony and I didn't bring it back inside before a cold night - she was too weak to do it herself.
When I saw it had been cooked dead from the frost, I felt so ashamed of myself, and so sad. And very angry at myself.
But there are plenty of little Henri K.'s Crassula in many places, including my home, and most people probably don't know that part of them is his legacy in a way. The kind of thought that makes me smile.
Two of the ones I feel in charge of keeping alive:
Funny how some people link plants with people...
And I'm not a bahá’í - though I wouldn't mind, I'm an atheist.
I'm not looking for any imaginary "reward" in a "paradise" that don't exist - my weight in Coca-Cola, 1,001 virgins, a disease-free world, etc. ... But I think that a straw can displace a mountain.
Good luck with your Schleffera, and remember: