IANAD but from my experience the doctors often have seen so much variation in outcomes that even they are never 100% sure about what to predict.
It doesn't sound good though and if I were you I would be making a working assumption that he might not get through this.
You don't say how far away you are but it may be that if his doctors are prepared to write you a suitable letter you would get permission to travel (check what the criteria are first to make sure they confirm the necessary facts in the letter).
In any event you can hopefully at least call/facetime or similar (even if your Dad can't take part, you can provide moral support to your Mum) and buy/arrange stuff remotely for them. Do the online shopping, send treats or practical things, produce shortlists of care agencies and get quotes etc.
If he has heart failure and is in the UK check with his GP as many local groups have a community heart nurse service. My Mum loved her heart nurse!
If it doesn't upset you too much, check everything is in order should he pass away. It was reassuring that Mum and I had discussed this sort of thing and we knew where her will was, where her paperwork was etc (and in fact I got 3 quotes from different undertakers for her funeral, just as she'd always taught me).
It's a very odd time and worse when you just can't be sure how things will go, but I certainly found it helped a lot to concentrate on doing what little I definitely could do to help.
