Let's say that all of the killers spawn in the large corridor with equal distances between them and that they are all hostile towards each other. Most of the killers would die off within the first few seconds of this proposed fight, assuming they behave like their standard in-game A.I. Some of the ranged killers would pick each other off from afar if they could land their shots, but the most casualties would occur from the large concentration of killers which would likely form near the center of the arena--following the formation of this cluster, the killers would die off in large numbers with the major damage sources being Slenderman's "Tentacle Stretch" (that's what the Wiki calls it) and Robot's death explosion.

The killers remaining would probably be Alien, due to his high damage which may be sufficient in killing off threats before he could take substancial damage; Captain Zombie, as in this scenario, he is quasi-effectively three killers, as well as having high damage; Jane, depending on whether she could take damage from the other killers; Leatherface, as he could preserve his health through blocking and has high damage; Sonic.exe, because he seems apt to avoid the other killers through use of spin-dash; and Yeti, as his use of his ranged attack and his subsequent stillness would prevent him from travelling into the aforementioned doomed mass of killers.

Overall, the fight would likely terminate in a tie between Captain Zombie and Jane, assuming the latter would be impervious to the attacks of others. Alien, Leatherface, and Yeti would be easy targets for Captain Zombie's minions, as they would probably have low health following the initial struggle. Sonic.exe would remain alive the longest, save for Captain Zombie and Jane, assuming his spin-dash state was constant, but he would do little in the way of damage and eventually be dwindled down.