Depends on the superstar and the position.
Can we acquire Paul George? Then give up Hayward.
Lillard? Then that makes Exum expendable.
Anthony Davis? Hey, as much as I like Favors, yes, I'd do that trade.
Also, to get your hypothetical superstar do we need to give up two of those players PLUS a couple of firsts? Well, then I think you look long and hard at doing that, How many championships did New York win by selling the farm to get Melo? How about Brooklyn and Deron, Johnson, Lopez and Pierce? Both those teams are in the crapper for many more years by trading away too many assets.
I'd exclude Exum from your list, though. There is no way anyone knows right now that he'll reach the level of the others, It's all conjecture based on his size and his good defense. But if he never develops offensively, he might not last as even the starter.
To answer your question, right now I'd consider trading Hayward. There's no guarantee he stays, And he'll command the most money. He's not an all-star, yet will probably ask for $30M/per. That's just not good bang for the buck. I'd rather get a DWill-like haul for him, Hayward doesn't have quite the accolades DWill had, but I think he could fetch a similar return: a promising young prospect, future pick and a decent SF to take his place.