What would Cordana Do. My thought is betray. She seems like the type.
Milli Vanilli, Bigger than Elvis
My thoughts are she should have been the Alliance legendary follower instead of Garona.
No surrender! 70 Vanguard - The Star Forge
Cordana's been with us since Cata that I know of. Unlikely she'll turn bad.
Thrall's going to be delivering some relic to Khadgar so he can use it to stop Gul'dan and Cordana will be there, tell Thrall to hand it over to her and that she'll see that Khadgar gets it. Thrall will decline, point out that she's been corrupted and kill her.
But really, it'll probably happen. Since the focus was always on Khadgar any supporting cast can be killed off without any worry. It's also a shame really, Wardens are supposed to be among the most self controlled forces on Azeroth, it's almost insulting that Cordana would be corrupted so easily just handling an artifact.