Just so we're clear, you're saying that a monopoly should be granted tax revenues to cover the loss of revenue incurred by a viable competitor emerging in the market, because they didn't anticipate that competitor emerging?
I think the OP is saying that they need to be paid back because they made a purchase based on the government's promise to enforce a monopoly.
If I paid a million bucks for a taxi medallion, and then 6 months later medallions aren't necessary--either because the government changes the law or because the government fails to enforce the law--I'm going to want a refund.
If I make any business decision that turns out poorly for me, I'm going to want a refund. It doesn't mean I should be entitled to one.
This is, ostensibly, what contracts should cover. The medallion issuer should be subject to a series of conditions under which the medallion purchaser is entitled to some sort of recompense if the issuer breaches those conditions. Entering into a purchase contract for an item that is literally the life and death of your career, agreeing to terms in which the other party basically says "trust us, we'll do what we promise so you aren't completely ruined" is a terrible way to do business.
