If your friend looks at his e-ticket receipt, he should see 1-3 lines of what looks like gibberish with letters and numbers. Somewhere in there, he should see MIA-LHR/XXXXX/YYYY.YY. The "X" is the fare basis and the "Y" is the base segment fare for MIA-LHR. If he multiplies that number by 75%, he will have the refund he is due (note that it is a refund, not compensation).