This isn't spoilers because it is pre update:
There is a lot of (probably true) theories about how 18 mercenaries and one Mann went into hell. Nine souls were able to make it back, while the other nine stayed in hell. The way I see it is that the Blu Mercs died outside of the respawn system, and this is why we only see reds in the comics post-helltower
If you want what makes me think this, listen to the bombonicon's lines for Hell.