(((Hugs, sweetie)))
I'm so sorry about your client's death. I'm sure you can accept things intellectually, but that doesn't make the sadness go away.
When I feel discouraged about not making enough of a difference I remember a story that I heard. It might be a little corny and you might have heard it before... but I'll write it anyway.
A man was walking along a beach that was full of starfish who had been washed ashore. He picked up a starfish and tossed it back into the sea. Then he did it again... and again.
Someone walking by said, "Why do you bother tossing those starfish back into the sea? Can't you see that the beach is littered with them? You'll never be able to save them all!".
The gentleman picked up another starfish... tossed it into the ocean and said, "Made a difference to that one.".