That doesn't make sense. You can still have an epic battle between Destroyer Maestro & God Doom without either of them perishing. It could have been quite epic and awesome, even if it ended in stalemate or Doom victorious yet Maestro managing to teleport out of there before getting killed by a being who wields the power of the Beyonders & Molecule Man.
If Doom loses some form of control, or if Maestro manages to break free of this wishing well, he's still gonna be able to possess the Destroyer armor and come for Doom & everyone else. And if that happens, everyone better stay the hell out of Maestro's way. Because he'll be out for blood & vengeance.
Anyway, while the issue was decent (mostly due to the art & Maestro's portrayal), it had the potential to have been truly incredible.
You can't have an epic battle if one side stomps the other. It would be just as one sided as when Phoenix Force Scott fought Doom. Again if Maestro attacked Doom he'd be dead. At least this way he's alive and when Doom does die, presumably Maestro is set free. Yes when he is freed he's right by the Destroyer and can back to trying to take things over.