iceman could try and constrict his blood flow and flash freeze him quick enough for rogue to drain some of his powers and cyclops to blast him at full force.
that will weaken him considerably
emma, linked to rachel can attack him mentally. it wont do much, but it should be enough to distract him a little.
rogue, colossus, wolvie and sabertooth attack him the weakened state, with iceman still freezing his molecules. mystique transforms into the hulk to help them.
bishop puts his weapons on full power to weaken despero still, while shadowcat attempts to crush his heart.
cyclops takes off his visor weakening him still and destroys half of the mansion along with it.
beast is in the control room firing all the perimeter weapons at full force.
psylocke get close enough to put a psychic katana into his brain. with rachel hitting him with psionic blasts of concussive force.
SNIKT! Wolverine manages to dig his claws in Desperos head. While Sabertooth plucks and eye out.
Despero finds enough energy to knock Creed out, almost killing him. But Colossus and Rogue are enough for him in his weakened state.
While the battle rages on for hours Beast has created a device to trap Despero in.
BAMF! Nightcrawler manages to teleport him into it.
The Sh'iar Imperial Guard already aware of the cataclysmic planetary threat, come down and teleport Despero to their empire where he is to be tried.
They sing and End Song for poor Despero
This is how the story could go, or Desp might win it, but its all up to Emma putting up psychic shield for her teammates.