But you've just pointed out the major flaw in the "passenger flights can work from Prestwick" argument. You suggest that Prestwick might have to buy back more Ryanair flights which can only mean the Scottish tax payer stumping up yet more money.
You don't need to "buy back" Ryanair. They used the airport in the first place because they got a better deal than GLA was prepared to offer. Now GLA has offered them a deal that they found acceptable. If this was to disappear, then PIK would become the better option again, and they may well switch a few services back.
No buy back, no discounts, just a continuation of the previous agreements.