I agree with Mr. Death that college groups split up. They have careers that take them to different parts of the country. It is natural that the group gets geographically disbursed.
The more interesting question to me is what happens next. Given the formor attacks, it is very likely that "some" of the alphas that moved away have become involved in the fight against the Formor. "some" might even have been captured by the formor. Add to this the fact that all of these individuals knew Harry rather well - and Harry started the Paranet -- means that heavy Alpha alumni involvement in the paranet is almost a certainity.
Given heavy involvement and given the fact that the Alphas are probably some of the most dangerous (combat wise) members of the paranet, the odds approach certainty that the Alpha alumni network is one of the cornerstones of Paranet self defense.
That has to become useful one day for Harry.