Since they never found her there or anywhere else, IDK if calling it a "scam" is accurate because we don't know. There's numerous areas she could've gotten into that radar wouldn't have covered. While I'm with you that LE did an extensive search, since she wasn't found anywhere I don't think you can really say that a particular theory is totally ruled out.
Really the theories IMO boil down to a few:
- Karlie tried to run away or accepted a ride from a yet to be identified stranger who took her wherever they took her and she is either living a new life somewhere or was murdered by said person or someone else in whatever new location she went.
- Karlie wandered off into the desert and surrounding area and died from the elements and LE searches missed her body.
- Karlie's stepmother or someone else in the house killed or hurt her and then covered it up.
I personally ranked them in order of likelihood based on what we know now and unfortunately do not believe Karlie is still alive - the chance of that is extremely low. #3 has never made any sense outside of the wilder theories posted elsewhere with 'evidence' such as "SM lied about her wearing jeans" and "SM seems shady". My signature includes Occam's Razor and #3 is the antithesis of that if you apply common sense and the fact that LE investigated both step parents repeatedly and found no evidence of involvement so I refuse to believe that the SM was this master criminal that could evade all investigatory bodies involved on the case.
So we're down to #1 or #2 or some offshoot of those. Had #2 occurred, I hear you that it seems likely that someone either via the search or after just out in the desert for whatever reason came across her remains which could be identified through DNA.
I normally don't opt for #1 at first because the sheer coincidence or happenstance that would cause a stranger with bad intentions to come across her at the exact time she left home in a drug-induced haze is up there, but I'm not sure what else even applies here.