Question: What happens to Mouss after beating up and robbing John? He doesn't get his comeuppance, does he?
Question: How does his father know what their final destination is?
Question: Would finding the button during the initial investigation (or even at the end) really have been enough to overcome all the evidence against her? It validates her innocence and the morality of the escape in the eyes of the viewer, just not sure if finding a button would lead investigators/prosecutors to say "yep, we found a button. She's definitely innocent."
Answer: It wouldn't have been that simple to say, "We found the button, she's innocent." It would however validate her story and reopen her case. Investigating further the cops may have found further evidence of her innocence.
Question: How did John Brennan know Laura would be transferred to a hospital?
Answer: John planted fake blood work for Laura indicating that she had hyperkalemia (increased potassium levels), a condition that is potentially fatal. She would need to be transferred to a hospital to be treated.
If Laura was was suffering from hyperkalemia, wouldn't the jail doctor have reported it before John planted the fake blood work?
She wasn't actually suffering from it. John had planted the fake medical report that the doctor presumably then read and acted upon by arranging for her to be transferred to the hospital.
I doubt the jail's doctor would be fooled by the fake medical report since Laura wasn't showing any obvious physical symptoms.
Many medical conditions do not show physical symptoms early on, but are detectable with tests. For example, people live with cancer, diabetes, heart disease, brain tumors, etc. for some years before experiencing any physical effects. The doctor read the results of Laura's blood test, and, as was standard procedure, had her admitted to the hospital, presumably for additional testing that could not be performed within a prison setting. Also, after some additional reading on the subject: hyperkalemia often has no early symptoms. Later symptoms are flu-like-such as muscle aches, physical weakness, nausea, fatigue, etc. That may be why John chose that particular condition, and it is something Laura could easily have faked.
I still think the jail's doctor would get suspicious since blood test results are not monitored and delivered to a county jail by an outside lab.
Suspicious or not, he would act in the patient's best interests. If the hospital blood tests come back negative, then he doesn't have a problem. If Laura dies in his care from an easily treatable condition which he knew about, it's goodbye career and hello huge malpractice suit. He would be fully conversant with the procedures used while transferring prisoners to local hospitals, including the very close security put in place, and he has no reason to think that someone is putting this incredibly elaborate escape plan into effect.
Speaking of a prisoner being transferred to a hospital, does that happen very often?
But don't jails, and prisons tend to keep a prisoners hospitalization a secret?
Question: Would the plan John used to help Laura escape really have worked? If not, then please explain why?
Answer: John's plan to help Laura escape would not have worked, because he would not have been able to plan ahead like he does in the movie. He would to know where Laura would be transported, and when and if she would be transported there. He would not have know any of that as the information is kept secret from the prisoners, and the public.
Even if he did find out Lara was in hospital, Lara would have been transferred to another hospital.
The movie attempts to cover this up by having him send fake diabetic results to the jail. This would not work because jails and prisons do not accept diabetic results from outside labs.
Answer: He read their airline tickets and probably the plan for their final destination is packed together with it.