I dont think anything is official yet. The extension was not granted for those aircraft but that just means that United felt that they could renegotiate better rates and a better contract. There has been a bidding war going on between xjt, tsa, skywest, and mesa for this contract. Your contract wasn't renewed but there could still be a "new" mesa contract with cheaper rates but with the same old airplanes. Same thing could very well go for the Dash's as well.
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you never know. The ASA 13 aircraft thing and the TSA recalls are not good signs for mesa to continue this flying.