Imagining that the castaways were rescued (and forgetting the three movies), which
two castaways do you think would be the MOST likely to keep in touch. Of course, we
are not including here the pairs Skipper/Gilligan or Thirston/Lovey, who would
automatically keep their connection.

I think Ginger would keep in touch with the Howells. Mr Howell did promise her to put her play on Broadway ;)

I think Ginger and MaryAnn would keep in touch, at least for a while. They were roommates and often seemed to behave like sisters.

I can see the occasional letter between the Skipper and the Professor as well - since they seemed to have a close relationship and had respect for each other.

I know this is just supposed to be two people...
But as a whole group, I think the seven castaways would keep in realtively good touch since they grew into a family. If you think about the show, just try to subtract even one character and think of how altered it would be and unbalanced the characters would be. Because in my opinion, the castaways individual quirks, mannerisms, personalities, ect where reflected off of one another. For example: Gilligan was bumbling while the Professor always had an answer for everything.