Well, considering guardians are relatively immortal (even if their ghosts are destroyed, others can revive them) and if they are working with the hive they have hive magic, vex time warping, fallen space piracy skills and cabal armies. Even after that, oryx can take some Spartans and add to the army. Halo- flood (killed easily, but not destroyed) Spartans (guardian can kill if elites can) unsc (human soldiers and the like) covenant (meh) friendly covenant (meh) and space artillery (Mac blasting the traveler will not kill the light, because each guardian is a source of light now). Halo has the halo rings, but guardians are both living and dead, meaning they are neither, the fallen are living, and the halo rings would wipe them out, the hive are neither living nor dead, so they would be fine. Vex are neither, would be fine. Cabal would die, taken are neither alive or dead or in-between, they would be fine.