My guess -- and I could be completely wrong, of course -- is that
Disneyland and California Adventure will stay in holiday season mode through January 6th, because it has become a tradition to end the season with the Three Kings Day event. Haunted Mansion Holiday will stay in holiday mode too, if that happens.
I think that this past January, Haunted Mansion Holiday stayed open a wee bit longer than usual, to accommodate the crowds heading to the parks for the debut of Frozen Fun (which was 1/7/15). So, in 2016, I'm not sure if Haunted Mansion Holiday would close down on January 7th (after Three Kings Day), which is a Thursday, or if it will stay open through that weekend and close on Monday, January 11th. Or, if the Three Kings Day celebration is skipped this time around, then Monday, 1/4 could be the closure date for HMH.
Whenever Haunted Mansion reopens, then It's a Small World Holiday will close soon after -- and that's usually after the MLK holiday, later in January.