That can happen but the fact that he was in hospital for a long time implicates them as they should have been making sure he had fluids and his electrolytes were ok etc.
If he is not taking in proper fluids without medical/carer intervention that is also a problem as the 24 hour care will not stay in place - what will happen when they pull back.
Fluids are a problem with older people, especially when they are on "water tablets" and this will effect the electrolytes, possibly leaving them potassium and/or sodium deficient which can sometimes produce dementia type appearance - it did with my dad and improved when corrected. It does not sort the problem, however, if he is not looking after himself properly anyway.
I hope they make the right decision sooner rather than later and before he does some real damage to himself.
Good to have you back Jim - have a good day x