I would agree with that if someone lost MB component at an assessment but in MIL case she has a lifetime award so I am assuming only death should stop her getting her DWP money for the mobility component I would have thought.
Try not to over think what I said. It was an example of a similar situation of when you said “it would be breaking the lease when payments were stopped” Its worth remembering mb frequently deal with these situations.
Your MILs lifetime allowance will only cease on her death, however the DWP could suspend her money if she is in hospital longer than 28days. Her DLA will then be reinstated from the day she comes home (you will need to contact the DWP to get it reinstated).