Would the characters appear in a new timeline? Quite possibly, I suspect. Whether it's Athurian legend of the latest DC reboot, popular favourites nearly always show up again. Whether they'd appear in new books...? More doubtful, honestly. If Disney stick by their guns and churn out a new Star Wars film every year forevermore, then that will be what drives the new timeline forward, not the books like has been the case in the past, so I suspect all spin-offs will be tied to whatever the latest film is, just like they have been with all previous films, so it'll depend on whether the latest film had a cameo of Thrawn or Pellaeon or whoever. It's the same as how TOR is unlikely to ever give us an Exile novel. A Vitate novel? Possibly. But the Exile was nothing more but a cameo in the game. Likewise, unless they decide to make an actual animated movie about Thrawn or something, I doubt we'd ever see them just go and rewrite the TTT for the sheer sake of it as they'll be wanting to maximise the merchandising opportunities for every new film, with novelisations, comics, and video games all tied into the newest movie like happened after the Clone Wars film. Fast forward a couple of years and you won't be seeing loads of TCW tie-ins and Darth Maul novels and comics, but loads of Episode 7 villain novels and comics.