"When All You Have is Worst, Worse, and Bad Options"
Don't do anything. Most everyone and everything in a 30-mile radius dies.
Open a portal and teleport Warmachine and the missile to the only extra-dimensional place he could access, the Astral Plane. An explosion there would most likely kill anyone who could access it within the same distance. With so many heroes here in the L.A. region, that would mean saving the general population of the region, but anyone with the slightest psychic ability would suffer.
Teleport Warmachine and the missile into space. Starmaster's teleportation powers weren't like Crossroads. He didn't open doors from one place to another. Teleportation happened when he slipped between dimensions, in physical contact with whatever he moved. If he wanted to do as Warmachine requested, Starmaster was going along for the ride.
Of course, when they arrived in deep space, all he had to do was take his hand away from Warmachine and return to the Earth. Starmaster would live. The people in the threatened area would live. Only Warmachine would die.
The answer was simple. Answers are typically simple. Ask anyone. It's typically easy to know what to do.
It's doing it that's hard.
And there wasn't time to come up with a better solution. It was now or never.
Starmaster placed a hand on Warmachine and the other on the missile. Together, they blipped into space, high in orbit of the planet. Just as quickly, Starmaster let his hands move the slightest micrometer away from what they touched and teleported back to the battlefield in Los Angeles. But not all of him returned. Part of him died in the explosion high above the planet. High enough that nobody could see it, but Starmaster could feel it as the devil ripped away a part of his soul.
He could have tried to teleport Warmachine away and left the missile, but Warmachine told him the explosion had already begun. Which was faster? Starmaster's ability to slip between dimensions or a nuclear explosion already in progress?
Starmaster would never know. He allowed Warmachine's belief to assuage his willingness to even try.