Our cat died a few weeks ago, and it was pretty sudden, we had been really busy with family events so unfortunately I wasn't able to fully perceive how far along she was, but she didn't eat well for a week I changed her foods, that worked for another week, then she barely ate for a week, and that was it.
Two years ago she almost passed away but I took her to the vet daily for a week and got her hydrated via an IV, at mid week the vet was like I've never seen a cat with "numbers" as poor as your cat's, maybe it's time to put her down, but my wife was on a business trip and I didn't want my kids to have to deal with their cat dying while their mother was away, so I just kept bringing her back to the vet and she bounced back so I figured it would be the right thing to do to bring her for IV again, since she wasn't eating or drinking water. I was really worried because I could tell she most likely didn't have much longer to live and I would rather she died with her family around her, but if I didn't take her to the vet and she died I would be mad at myself because I didn't try every last thing, particularly when the IV brought her back from death's door last time.
Well I sent her to the vet and she didn't make it back, so I felt pretty crappy that she died without her family because they sent my wife home while they were giving our cat the IV.

My boys really made me proud, my kindergartner was really compassionate to our cat, she was really laboring to breath and he sat by her and sang a really soft song to her which relaxed her to the point where I got nervous because she then was barely breathing and I wasn't sure if she'd be about to muster up the energy to breath more normally again.
Right before my kindergartner and wife took our cat to the vet for the last time (she didn't make it back home) my toddler came rushing over and said, "Wait Daddy I've got it," and pulled out our play doctor's set and tried to treat our cat.
The older boy has a pretty full understanding of what it means to die and so he took it harder, the little guy still asks when is "Whinnie is coming back?" To which I say she's lives with God now, and It's really great there, and try to be convincing as possible.