I am so sorry, OP. I couldn't stand to be in your position. You asked for personal stories, and what happens the day a person dies, though, and I can at least offer something about that.
Last year I was with my granddad when he died. He had an aneurysm, and rather than the bolt-from-the-blue death the doctors promised when it ruptured the damn thing sprung a leak and he died very slowly.
So, being in the room. It's hard. He was in a private room in A&E and they had switched off the monitors. He was under an inflatable plastic blanket. When I got there his eyes were open and he saw me, I think (hope), but when they closed they didn't open again. He was on oxygen.
I couldn't stay in there the whole time. Me and my dad went to McDonald's. I hoped he would die while I was out of the room. He was still alive when I got back.
He was still alive. He occasionally moved, groaned a bit I think. The nurse went to get him more morphine.
At the very end we (Mum, aunt, dad, me) stood around his bed. I held his hand. His breathing was like shallow snoring.
At one point he started to bring up red/brown mucus (he smoked for over 70 years) and a nurse came in to suction it out. Mum stroked his hair, my aunt had his other hand. I remember I swung from huge, overwhelming despair to absolute, beautiful calm.
At some point I realised one of these rattly breaths would be his last. His breathing slowed down, sill shallow, still more like a snore than anything else. And then he didn't breathe in again. I was aware of his fingers being cold, like he'd just been outside in the snow.
A person changes after death. Almost immediately he looked completely different. Sunken, I suppose. His hair even looked different. We stayed with him, crying on and off, until the nurse came to take us to the Family Room.
Since he died in the hospital we had to wait for the police, which was bad. We were quiet, crying, not crying. Trying not to think.
When I got home it was 3am. I went to bed. The next day I had a dentist's appointment and had to go to work.
Things will hit you at odd times. You may cry till your eyes hurt, or bruise, or you may not cry at all. There's also a lot of really mundane decisions and awful paperwork. And worst of all, the rest of the world just keeps on going.
I hope you get through this okay, OP. It's not fair.