Neither Scott nor Magneto have genius level intellects that could help deal with the collapse of the multiverse. Hank is the 8th smartest person on the Marvel Earth and helps runs the Jean Grey school.
Not so. Remember "Classic X-Men"? It was a re-print book the re-packaged the early "A-New All-Different" Uncanny X-Men issues starting with #94. As a bonus, each issue had two or three bonus pages written by Chris Claremont inserted into the main story as well as an all new backup story.
In the issue that reprinted #125, Claremont added a sequence with Magneto corresponding and exchanging ideas with Stephen Hawking (One can only assume that Dr. Hawking didn't know that the man he corresponded with was actually Magneto). Surely this indicates genius level (at least) intelligence.