We had a missing hiker case near me (also a thread for her here on W's)
Similarly last seen early on a Sunday am leaving her house for a hike (but driving to the location and her car was there). She made contact with her husband 3 hours after leaving the house, then no response. LE and volunteers weren't involved by that afternoon searching.
She was ultimately found very, very near the main entrance to the preserve, right by the only restrooms, but just off a few feet in a technically "closed" portion of trail.
Much of the search staging was done very near where her body was found, and this is in the heat of Phoenix, so very similar highs to the current temps in Australia right now.
Even with search dogs, drones, helicopters, searchers on foot and horseback, she was not noticed (nor was there smell - again, similar heat, Kathleen was just found 4 days later so it didn't go on as long) until Wednesday.
So IMO it's entirely possible. Though maybe by now if SM were close a smell might be more obvious.
A hiker in Cave Creek, Kathleen Patterson, 60, has been missing for days now after she was last heard from while on the Spur Cross Trail on the morning of Sunday, Sept. 25.
www.fox10phoenix.com