I personally wouldn't take Austin because he ain't all that and a bag of chips, but as for your question...
I've been hearing that when Haynes is back they will either send Reitsma or Reith down. If it's Reith, they'll slide Reitsma into the bullpen. So Austin should be safe for a week or so, but then you have Dempster probably starting again soon, after pinching a nerve in his neck. The question for the Reds then is do you send Austin back down, or push Riedling back to the bullpen and drop a reliever?
It was not definite, but it was looking like Austin would be sent down because manager Boone seems to like Riedling and because Russell Branyan was coming back soon. Instead of dumping Wily Mo Pena, they'd send down Austin and drop their pitching staff from 12 to 11.... Now yesterday Barry Larkin got hurt again, and if he has to go on the DL, that'll leave room for Austin for another 15 days or so.
This is all speculation, and the best theory is, if and only if Austin pitches a great game in his next start, look for the Reds to find some way of trying to keep him up here for the time being. Otherwise, he'll probably be gone in a week or two. My vote is a no to picking him up.