My guess is it actually has nothing to do with winter as that would be too on the nose.

Rather it is the meaning of riding out a period of hostile environment or storm somewhere else. The idea of wintering is to go to a place that is warmer cause you don't like the cold bitter winter.
So it doesn't have to be the cold bitter winter, it could any such season that is unappealing or hostile in this context.
Birds fly to warmer places in the winter.

So it could be people from the 9th who went to other shards to escape the lightning flood while they came up with a solution.
Or it could be the other Ascians or Ascian adjacents who didn't like the idea of a rejoining but couldn't stop Emet and co and were hiding from them.