February 2016
I assume this is going to drop into the abyss of the internets.... but...
Is there anything that I can do if I've already made progress/purchases on a guest account but did not link to Game Center? I seems crazy that I'm just stuck waiting for my iPad to die and lose my progress.
March 2016
The same thing happened to me, there is nothing they can do. I talked to so many people about this and eventually just gave up and started again
March 2016
I found a fix for this, detailed here: https://forums.galaxy-of-heroes.starwars.ea.com/discussion/3/regarding-lost-accounts/p2