Well, that's IF not WHEN. If you don't think Conor has a chance to win this fight, then you're just a fucking idiot.
But Khabib definitely has a great chance to win. If Conor loses, it will look ugly, especially in the later rounds. I don't think Conor will lose his star power, at least not right away.
I mean, your question was kind of already answered. He lost against Nate Diaz, then sold 1.6 million PPVs in the rematch against Diaz. So if anything his star power increased. The real question is, how does Conor maintain his star power if he loses to Khabib a 2nd time*. Because if he loses 2-3 fights and looks "done", then he will definitely lose his drawing power.
If Conor loses to Khabib, he will likely fight Nate Diaz again, a fight I think he wins. From there, Conor can beat Poirier and Tony Ferguson easily. Neither of those guys have the takedowns to threaten him, and Conor destroys them in the standup.
The only 2 fighters at 155 I see giving Conor a hard time are Kevin Lee and Khabib, specifically because both have great takedowns to nullify Conor's standup. McGregor simply has the best standup in MMA. If you don't believe that, then you're deluding yourself.