For the ending, I see there being several possibilities:
(Here I will refer to the cataclysm that purges Eschalon's surface of its life as the "lesser" cataclysm, and the purported shattering of Eschalon itself (as a result of preventing the lesser cataclysm) as the "greater" cataclysm.)
1: side with Erubor
1a: Erubor is correct; both the lesser and greater catacylsms are averted, the Orakur never evolve
1b: Erubor is wrong; Eschalon is destroyed after the greater cataclysm; everyone dies and the Orakur never evolve
1c: Erubor is lying; neither cataclysm will happen, and Erubor becomes god-king of Eschalon
1d: Erubor is lying; the lesser cataclysm WILL happen, but Erubor rules the aftermath; the Orakur evolve
1e: Erubor is wrong; the lesser cataclysm CAN NOT be averted, safely or not; the Orakur evolve
2: side with Malkur
2a: Malkur is correct; the lesser cataclysm happens, but the Orakur evolve and survive
2b: Malkur is wrong; the lesser cataclysm COULD be safely averted, but is not; the Orakur evolve and survive anyway
2c: Malkur is lying; neither cataclysm will happen, and Malkur becomes god-king of Eschalon
2d: Malkur is lying; the lesser cataclysm WILL happen, but Malkur rules the aftermath; the Orakur evolve
1a and 1b are not consistent with a stable time-loop because the Orakur clearly exist. 1c and 2c likewise preclude the existence of the Orakur. 1d and 2d are both possible, but in the case of 2d, the question is raised of why Malkur wasn't already king of the Orakur in the future, considering his likely immortality. (If he survives the lesser cataclysm in 1e, a similar question arises.) If Erubor is capable of extending his life indefinitely, the same question is raised for 1d. 2a and 2b are effectively the same in their end results: whether Malkur is correct or not is wrong as long as he prevents the lesser cataclysm from being stopped.
The orrery in Old Moonrise and Karamiklan both predict the lesser catastrophe, and the Orakur definitely exist, so it must be assumed to have happened.
Thus, assuming that Malkur's intervention caused the Orakur's time machine mishap in the first place (cf this post
), 2a and 2b are the only possiblities consistent with a stable time loop: all life on Eschalon other than the Dwarves that will become the Orakur are in fact doomed. It is impossible in this case for the protagonist to side with Erubor without breaking the time loop, with any consequences attendent to that (if any).
So far in this discussion, the idea that Malkur's actions may have caused the original time machine's problems (sending the Orakur time travel party 200+ years further back than planned) seems to have been largely ignored, which is curious, considering how much sense it makes.
3: the Orakur are not actually time-travellers from the future, but rather come from somewhere else
This possibility is basically that Malkur and possibly also Erubor (unless Erubor himself is misled) are trolling you, the protagonist (and maybe Erubor), big-time, for kicks.
2a and 2b seem the most likely to me, but personally I prefer 3.