That edit you made was incorrect completely. Do not keep editing if you have no clue what you are talking about. It was not an illusion in Yoda's mind, if anyone else was there they would have seen it. It was simply an illusion. Thanks.
You should know that Stass Allie has not yet appeared in TCW. It was Adi Gallia we saw in "A War on Two Fronts." It's been repeatedly confirmed that the Onderon, Youngling, and D-Squad arcs all take place before Revival.