There was still a possibility that Necaxa's relegation to Mexico's second division (confusingly called Primera A) could have been averted had Salamanca won the Clausura tournament, and then won the promotion playoff against Querétaro. Because Salamanca does not possess a license (called FMF Certification) to play in Primera, they would have received the $2 million prize for winning the promotion playoff but no actual promotion. (I haven't been able to find more information about FMF Certification, but I believe it works in the same fashion as Associate/Full Membership in the J-League. As in Spain, reserve teams cannot appear in the top flight with their parent club.)
At any rate, Salamanca lost to Club Tijuana 4-1 on aggregate in the semifinal round of the Clausura playoffs, and as Tijuana and Mérida have licenses to play in the top flight, Necaxa are "doomed" to second division football. I place "doomed" in quotes because there are rumors of a restructuring of the lower division that would allow Necaxa to stay, and I still believe a purchase of the promoted side's license is not beyond the realm of possibility.
In short, if Necaxa play more than a minute of second division football, I will be very surprised.