I'm sorry. 
My mum was diagnosed quite late at 79, and she managed 3 years (mortality does depend somewhat on age at diagnosis, I believe).
The first 2 years were what you'd expect - becoming confused in usually familiar surroundings, missing appointments, getting lost, constantly leaving her pushbike in town! Withdrawing from helping out at the church, feeling that she was unreliable etc, and "confabulating" - coming out with outrageous stories she believed to be true but which couldn't possibly be.
You tend to get a big "dip" at some stage, and for mum it was some kind of fall along with a UTI (we weren't there so don't know what happened, and she couldn't remember) - she had a terribly painful lower back. She never really recovered her mobility after that, although the pain improved - it was as though she'd forgotten how to walk, she could no longer lift her feet up. She used a walking frame but started to fall a lot more frequently over the next few months.
The wandering then started - she'd get confused in her flat and wobble off down the corridor in her nightie with her frame. A neighbour (she lived in a retirement complex) found her down in the stairwell in the dark, I have no idea how she made it down the stairs from her first floor flat. This is making me emotional.
The warden started putting me under pressure to move her into residential care, even though I had carers going in twice a day - I had set up cameras in her flat so we'd know if she fell, and put notices around to try to stop her leaving. I didn't really know what to do, I knew she wouldn't want to be in hospital.
I upped the carers to 4 times a day, but she somehow always toppled over or disappeared between visits and before I could get to her (I was 30 minutes away). This all happened in the space of about 8 weeks. Just before Christmas 2019 she was found face down on the lawn in the dark and the pouring rain one night, telling her rescuers (a passing ambulance crew) that she was trying to bring me some biscuits.
I managed to get her a "respite to permanent" place in a care facility near me, but they couldn't take her until new years eve. The night before, the camera caught leaving her flat at 1am, in a nightdress and with her frame. She activated her wrist alarm at 2.15am, and she'd just walked to the other side of the development and sat down - indoors luckily.
I was so relieved yet sad to see her go into care the next day. She declined very quickly after that move, which is common - she generally thought I was her sister, and I played along. As the weeks rolled on she wanted to know why her mummy and daddy weren't visiting her (dead and gone for 40+ years). I would say they'd gone shopping and would call in later.
In the end she suffered a significant UTI which developed into sepsis, and she passed away in May 2020 after only 4 weeks of being very sick. I was able to see her once when she was lucid enough to give me a big bright smile, and I told her what a wonderful mum she had been and that she could go whenever she was ready. I saw her once more a few days later when she wasn't really there anymore, about 10 hours before she died, and then a few hours afterwards.
I can't dress it up - it's stressful, it's difficult, and it's heartbreaking. But when you're right there in the middle of it, you just deal with it, because that's life. You get very accustomed to a new version of the person as they change. When they go it isn't a shock, and you're mostly glad for them that they don't have to suffer the indignity of it all any more. I was happy for her that it was over.
The grieving comes in fits and starts, much later, when you remember the pre-Alzheimers version of them.
I hope your uncle still has some good quality time left - don't fight it, try to go with it and help him feel normal and safe. I hope I haven't upset you - sending my best wishes.