largely impossible to tell from the outside. Critical medical treatment has gotten very good at keeping people barely alive. The idea is that you keep someone's vital organs working just long enough for treatment of the underlying condition to work or for the condition to pass but sometimes- maybe even often- it just ends up keeping someone technically alive until either they pull the plug or everything decompensates past the point that can be dealt with. Especially if it's someone with multiple comorbidities.
Someone can have a heart that is so fucked that they won't be able to stand up but they can be 'alive' on 4 vasopressors to keep their blood pressure above zero for quite some time. Then, because those medications fuck with blood flow (to keep organs working), little piggly wigglies leave for market forever (extremities start dying). Then the kidneys shit the bed because, hey, who needs those? More major medical interventions come into play. No way of leaving the hospital, no chance of a transplant, better to load up on morphine and ativan at that point.
Or- maybe he makes it through with a ticking time bomb and the ICU is out of an abundance of concern.