I've been following this for a lot of years. Forgive me if this has already been thrown out there.
What if the Saturday night/Sunday SAR was to Ewasko as China Lake was to the DV Germans?
For a moment, let's (1) accept that the ping occurred on Sunday at 0630 (about an hour after sunrise) and (2) disregard the ping radius for now.
Let's also accept: (1) The ping on Sunday morning would indicate that Ewasko was more than likely mobile at that time. (2) Ewasko would have expected a SAR by end-of-day Friday. (3) The SAR didn't begin until Saturday evening.
So, one of two scenarios occurred:
1) With no signs of a SAR, Ewasko began to attempt self-rescue on Friday evening but didn't get into cell range until Sunday morning, when his phone got one solitary ping out at an opportune moment that did not happen before and did not happen again. IIRC, this has generally been the accepted scenario, although met with perplexity. (I have trouble getting my head around it, to be honest. It's a lot of variables.)
Or
2) Ewakso decided to wait through Saturday for a SAR, planning to attempt self-rescue on Saturday evening. This hinges on him knowing a SAR would happen and potentially rationalizing that Mary didn't notify authorities until later than he expected.
My sense is #2 happened. He had limited water and got into a bad situation sometime Thursday: injured with limited mobility, lost, no cell signal, and further out than he expected to be. He decided to hunker down until the SAR came, conserving energy, water, and supplies. Any movement would occur at night, rather than in the day, again to conserve energy, supplies, and water. Then, whatever he saw or heard on Saturday evening triggered the cell phone ping on Sunday morning. Did he see or hear the SAR efforts? Did he realize that he was much further out than he realized and that he would not be found in time? Did he move closer to the SAR efforts overnight on Saturday, then try to use his cell phone as a signal mirror after sunrise on Sunday morning? (FWIW, the "lights in the saddle of the ridge" reported in the FOIA narrative are too coincidental to be a coincidence, and I wonder about that a lot. Was he trying to signal them?)
If my expanded #2 premise holds true, then where would Ewasko have reasonably been (again, disregarding the ping radius) where (1) he could see/hear/notice the SAR on Saturday evening but (2) be out of range of them enough for him to decide to move toward them and (3) be out of range enough for the SAR to not notice him. Is there a place that makes sense and hasn't been thoroughly searched yet?
My two wild theories would be:
1) he parked at the wrong trailhead (he had written directions in his car, indicating he was not overly familiar with the park) and decided to hike to his actual destination (all I can think is Keys View or Queen Mine/Lucky Boy, which is crazy). I've done that many dumb times but not in a desert in the summer.
2) he meandered down toward (not to - just toward) Coachella Valley Preserve through Covington Flats. The ping radius actually intersects down there in the jagged canyons, IIRC. The rock cairn and other clues discovered in Covington Flats may point toward this, but it's inexplicable for someone to go into that unforgiving area.
This is probably just noise; this one has been bugging me again after a lot of months, and I saw some activity here. So I'll echo others and say how incredible every effort has been to find Bill Ewasko, especially after all this time. Truly incredible.