Here's my optimistic case.
Joey's value is just something that accrues really, really slowly. That's less valuable as we get down to 30ish games left and even in a short series. Mona is perfectly fine as a short-term replacement. He'll miss some outs, but your other middle infielder is a genius with the glove, so I doubt it costs us a win.
There's also some big gaps in the advanced metrics. DRS has Ortiz at -2 while OAA has him at +7. I don't buy Mona as in the same ballpark as Ortiz, but at least one advanced metric seems to think the two are very similar.
Still, speedy recovery to Joey. When every base runner is a rally in the playoffs, that's the guy I want up the middle.