Sorry to hear you’re not getting any answers yet.
Can I ask whereabouts in the country you are? Does your hospital have a dedicated cardiology department? If so you should be able to speak to a member of the heart failure team at least.
WRT staying in for longer, while it doesn’t seem like it right now it might actually be a good thing, because it might give the chance to do all the things they want to without him having to go on to several waiting lists.
While my entrance to hospital last year was extremely traumatic, they acted to get all my procedures (mitraclip, ICD, all the scans) done while I was in there, and I didn’t get discharged until all that had been done. And while it meant I spent six weeks in hospital, it also meant that when I came out I didn’t have to then go on to waiting lists for all those procedures, and come out feeling as crap as when I went in and not knowing when that would change.
Temperatures can also be normal. The first time I was in hospital we used to joke about the fact the nurse would come round in the evening and say “paracetamol tonight?” 
and last year they did the same and I’d say “yes, I have chest pain.... erm I mean pain in my chest from the compressions.”
They may not even tell you exactly when he will have the MRI if he’s going to have it while he’s still in there. I didn’t know until the morning that I was going to have one, but the consultant who did it was lovely, and actually took me back to the ward himself.