Hello folks,
Like Bill said, TDA does not cover exotic games.
However, I am used to run those games so here is how I would rule it :
Win the button is all about the fact the players in the blinds do not want to pay again and again and it provides a lot of action when everyone folds to the button. So, if the same player keeps winning the button every hand, "someone has to do something" to stop him.
So being the BB three times in a row is possible in this game, and it happens often.
Also WTB is a game where position are determined by the button position and not by the big blind (in tournament, BB moves 1 occupied seat to the left and determine the SB and BTN position.
That means in WTB you should always have a SB and a BB.
So to give a straight answer to your case :
Seat 1 : Player A won the BTN, he is the BTN
Seat 2 : Player B is out, Empty Seat
Seat 3 : Player C in now the SB
Seat 4 (if not empty) : Player D is now the BB
To extend the case, if the next hand Player Wins the BTN again and a player is seated in Seat 2, Seat 2 will enter as SB wherever he comes from (other table, breaking table, registration...). This is used to prevent the case this player will never get dealt in if the player on his right keeps winning the button (infinite loop).
Again, all I wrote is for Win the Button only =)
Cheers