If the Bucks draft Embiid, he's a bit of a project with injury concerns, so the smart idea would be to go with Sanders as the starting center going into the season and give him a chance to rebuild his value while bringing Embiid along slowly, trying to trade Sanders only when they are convinced Embiid is ready to take over the starting role.
Sanders for Wallace and a pick seems more like a trade you might make in 2015.
What about Keith Bogans, Joel Anthony, and a pick for Sanders? This would be Plan C or D for me because I'd prefer going after Asik, but if Bogans' contract isn't used anywhere, then giving the Bucks some salary savings plus a guy suited to being a stop-gap short-term starter while they wait for Embiid to develop would make sense.