So under the October FAQ, a wildcard can continue to copy the TA of a character even after that character gets KO'd.

"Q035: If a wild card is using the team ability of a friendly character and that friendly character is KOd, does the wild card retain that team ability?
A: Yes, the wild card would retain that team ability until it chooses a different one."

What changed in the rules to make this possible?

This:

Wild cards.
Wild card team abilities are special team abilities that allow a character to use any team ability possessed by any friendly character on the battlefield. A character with a wild card team ability is called a wild card. When making use of a team ability they do not possess, a wild card does not gain the team symbol of the team ability used. Wild cards may use only one team ability per action. During your turn, you must declare any change in wild card team abilities when you declare an action. During an opponent’s turn, you must declare any change in wild card team abilities after your opponent declares an action and before the action begins—for example, after an action is declared but before an opposing character moves or attacks. Wild card team abilities may also be changed between actions or at the beginning or end of a turn. Wild cards retain the team ability they last used until they use another team ability. If the declaration of a wild card team ability makes the declared action impossible to perform—for example, if a line of fire for an opponent’s ranged combat attack can no longer be drawn to the wild card—treat the action as though it was not given and choose a different action. The wild card, however, must continue to use the declared ability even when a new action is declared.

If a figure that is wildcarding the TA of a KO'd figure is mind controlled and the team ability is changed by the the mind controller, when the figure reverts back to the owning players control, can it once again choose the TA of the KO'd figure?

It should keep the original TA as the figure that has been MC'd is now in control of an opposing player, once the action is over for that wildcard, and ownership reverts back to the other player, the figure will regain it's original copied TA.

it shouldn't... outwit and mind control don't work that way.

it should keep the copied TA that the mind control gave it until it changes again. and it couldn't go back to the KO'ed figure's TA for sure.

when you mind control a figure with outwit and use that outwit against its own teammates for the mind control action the owner of the figure doesn't get to retarget the outwit until his next turn. it doesn't revert back after the MC is over and i don't think the wildcard MC would either.

Also, to support Cornsilk, if I MC your figure and shut off his team ability, it stays off until the end of the current turn, even after it reverts back to the original owner.

Since I cancelled the WC ability, he loses the team ability he was copying, and since that team ability is no longer on the map, you can't copy it any longer.