Not sure what news would have led you to believe that the job was Zumaya's by default... sure, at some point in the future he's the closer-in-waiting, but there's never been any indication that Jones' isn't Leyland's man, even in the worst of times.
This season Jones is steady as ever. Only one blown save in 17 opps (well, okay, 2 after today), and sporting a 4-0 record. Sure, the 4.90 ERA and 1.5 WHIP is awful, but it's no different than it's ever been. That's just his style, and obviously the Tigers' brass are more than happy to let him keep spitting it.
Zumaya will not take over the closer's role this year... even if the Tigers are out of it going into September. There's simply no reason for it.
If the Tigers are considering changing (or even concerned about) anything in their bullpen, they're gripping over Rodney's setup-antics (everybody sitting on his changeup and watching his fastball hit the backstop). Everybody else has pretty much been doing their job to this point.