It sounds like you and the social worker had a misunderstanding. Certain specific Medicare Part A inpatient hospital benefits may run out temporarily, and one part of Medicare Part A's
long-term hospital coverage may end, but overall Medicare coverage does not become exhausted. The same is true for Medicare Part B coverage of outpatient medical care -- some benefits (like physical therapy, for example) may have a yearly limit but they are renewed with the following year. Also, for people who have both Medicare and Medicaid, the Medicaid benefits fill in the gaps in Medicare coverage, including when a specific Medicare benefit runs out.
Because it was a hospital social worker who gave you the information, he or she might have been referring specifically to your brother's hospital coverage under Medicare. The amount Medicare Part A pays for an inpatient hospital stay is based on what's called a "benefit period," which begins the first day a patient enters the hospital and continues until the patient has been out of the hospital and a Medicare-covered skilled nursing or rehabilitation facility for 60 consecutive days. So, during his last benefit period, your brother may have "exhausted" one category of Medicare Part A hospital payments, leaving him with copayments to make. But that's when Medicaid benefits kick in, paying the amounts that Medicare doesn't pay.
It would be a good idea for you or your brother to get back in touch with the social worker to find out exactly which benefits he or she was referring to. Also, Medicare will send your brother what's called a Medicare Summary Notice that explains what bills it has paid for him and what the state of his remaining coverage is. Your brother can also contact his Medicaid case worker to find out if there are any limits on what Medicaid will pay for his care.