I hope enough folks commented on the survey regarding a return to Olde World that it happens some day.
I don't think Age of Sigmar will be dropped to bring back Warhammer Fantasy Battle in the World That Was.
I suspect there is a possibility that apart from anthologies and re-issues there might be occasional new Black Library fiction, but that'll be even less frequent than new Age of Sigmar fiction, and nothing looks to be in the pipeline.
After that, it's a possibility that they may bring back a sort of WFB either as a special edition limited book, as well as a limited armies book more likely under the Forgeworld or Specialist Games brand, and tied in with occasional Made to Order releases of old miniatures.
I do think when Specialist Games get around to making Mordheim it will be set in Mordheim, and that may be their likely way of exploring the World That Was.
Other than that, Warhammer Fantasy Roleplay 4th edition is arriving this year by Cubicle 7, and with a ruleset that looks set to be their idea of an improved 1st/2nd edition, and from clues set just before The End Times.