Cashel's was in a highly competitive environment, whereas the closure of Beamish means that Diageo pretty much own the entirety of Irish ale. The only reason they'd ditch Macardle's, IMO, was if they decided to convert its drinkers to Smithwick's, and I suspect that's too much work for too little return.
Macardle's, like Satzenbrau, will cling on for a while yet, I'd say.