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Yes, there is.
Anyone holding unused tickets can mail them, along with a receipt (if any) and contact information (name, address, date of purchase, and reason for the refund request, which is obviously that the monorail is broken), to Refunds, Transit System Management, 3720 Howard Hughes Pkwy. #200, Las Vegas, NV 89109.
If you want further information, call the monorail system at 702/699-8299 and press 1 for customer service.