As reported previously before 'Gamma World' aired, Avengers:EMH will be apparently staying on Sundays at 10am/9 Central for Disney XD. This is not a holiday fluke, but a schedule shifting.
Sunday, December 12th's episode will be called "459." You can verify this for yourself by checking Disney XD's schedule. My updates are coming via my DVR which I then crosscheck with Disney XD's schedule to make sure it's not a hiccup from my provider.
Sadly the schedule currently stops on Wednesday December 15th. Feel free to check it every so often though, as they update as days are knocked off. Plus checking it is exactly why it's provided by Disney.
Just a reminder, but this Sunday is the next new episode. It is called "Masters of Evil" and will be airing on December 5th at 10am/9 central.