I am a participant in this situation as I am not going to the UK to see her ever, but there are two things to think about.
If you paid for your concert ticket via credit card, I would imagine that the cc company would help you if you dispute the charge.
A second point to consider is unclaimed property. Every state in the USA has an unclaimed property department that entities are mandated to turn over unclaimed property - an example would be unredeemed gift certificates, uncashed payroll checks, perhaps unused tickets would be eligible. Check it out with your state unclaimed property division.
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