This is a list of Astronomica's six endings.
Ending 0: Awaiting another Inflicted
After slaying the Rot-crazed Astartes without the gate to Orbeque's outpost, you realise your own insignificance in the task at hand, and choose instead to stand guard upon the brink of the outpost and await the coming of one more worthy.
Ending 1: Rash maneuvre
In destroying your only hope to unlocking the past, you destroy your hope in retrieving the Carrion Christ. In despair, you lay down upon the stone and await your eventual end.
Ending 2: Welcome to the flock, child
You fall into the arms of the Carrion Christ, and he, accepting your weeping pleas of forgiveness, makes you a captain over a thousand of his legion and you prepare to vansih into the stars.
Ending 3: For we all come to Convergence to die
Hazreb fades into the stones upon which he was born and Convergence immurimates those who sought to destroy its master for ever.
Ending 4: Together do we march (DLC only)
After being forgiven, you bring the XIIIth legion, your XIIIth legion into the fold of the damned and the phantasmic superlegion filters back into the stars.
Ending 5: Saving light of the XIIIth legion (DLC only)
You are saved by your primaris Astartes, who draw you and Orbeque from the depths. Together, you begin the eradication of the damned, and so destroy their curse upon the Imperium.
None of these are necessarily canon, though I personally prefer Ending 3.