I could be wrong but I think many in this thread are overestimating the type of return Mateo might deliver in a trade, because I'm not sure about how other GM's would value his body of work. Yes, a gold glove, 800 OPS, 5 WAR lightning bolt is highly coveted. But Mateo has yet to show that he is that player for the long run.
I personally would try to trade him at the deadline if Ortiz shows that he can hit ML pitching, but I wouldn't be shocked if the return is underwhelming. (Unless there is a GM out there who overpays)