Well, my Mum had (I think) 4? hospital admissions with heart failure over a couple of years.
The first two, they managed to buff her up and turf her out to go live her life.
The third one, she was in for weeks, finally got out with a portable oxygen machine, went to an all-weekend event with it trailing around after her... And was back in by the Wednesday. She never came home.
The trouble is: - fluid retention interferes with respiration, and you need that at all times to stay alive. Heart and lungs you can't do without. So, they throw diuretics at you, and that's tough for the kidneys.
Eventually she had a consultant come round saying her kidneys had failed and there was nothing more they could offer (+)
When kidneys fail, eventually the electrolytes in the blood get out of whack. This plays merry hell with the electrical system which keeps the heart rhythm going. And see above - no working heart, that's IT.
That's what happened to Mum - she went off her food, got diarrhoea, was moved into a side room (§).
We were visiting and she needed the commode, so the nurses shooed us out. A couple of minutes later they came sprinting out to get us - she'd had a heart attack and passed away a minute or two later with us by her side.
The reason the course of the disease is not that predictable is they can buff you up a bit, and then you're ok for a while... until an infection, or overdoing things, or SOMETHING triggers "decompensation" (fluid buildup, breathing problems, can lead to cognitive problems as you're not getting enough oxygen...and e.g. ulcers because fluid buildup is hell on the skin).
It wasn't the worst way to go. Aside from a UTI-induced delirium episode, which was worst of all but only lasted a day or two before they put her on a new antibiotic and fixed it) she was "herself" the whole time. The last couple of days her legs were terribly swollen and they couldn't do anything, but she didn't seem to be in pain.
Work let me do 4h half days starting at 0730 and take the afternoon off, so between me and her partner she had someone come in every day. I dropped everything else and put on about 20 pounds. Work offered caring, unpaid and bereavement leave so I was lucky there.
I think you just have to do what you can and if your best guesses don't work out, put it aside and concentrate on the present and future.
(+) In hindsight I have no idea why they kept her on the ward doing tests and even sent OT round (who were LOVELY) to help her with walking a bit, rather than getting a palliative care package together so she could spend her last days at home.
Maybe they still entertained some distant hope of turning the situation round? Maybe there was a tacit agreement that she was best off in hospital where she could get (relatively) timely care for any distressing symptoms? Maybe they were supposed to, but the message got lost?
(§) THEN they called in Palliative Care with a view to getting her home early the next week.
But an overheard conversation suggested they thought she wouldn't last the weekend, and they were right.
I'm not too sorry about this as she was generally receiving good care where she was, and I've heard some horror stories about things kicking off when someone is in their last days at home with only pop-in carer/nursing visits.