Possible/plausible endings to TUC.
Lawful-Good Kellhus wins: he defeats the consults, learns some more magic, goes to the outside, defeats all evil, and the universe is saved - permanent heaven on earth (and everywhere else).
This is the version that people who think Kellhus is the good guy want/expect - at least as far as I can tell. IMO, this is the worst possible ending for the series as a whole. Really ruins everything. "Happily Ever After" is not the correct ending for The Second Apocalypse lol.
Neutral/Neutral Kellhus wins: Kellhus defeats consult, learns all the tekne things, leaves Earwa behind to its own demise and goes into the Outside, learns/conquers all the things there (turning it upside down in the process) and move on.
This the the "Kellhus is a means" accumulating machine" ending (the phrase coming form Bakker to describe what Kellhus is): accumulating means (power) for the sake of accumulation and no other purpose. This ending is uninteresting to me. You basically are left with everything Kellhus touches is consumed and left in ruins and the world(s) just kind of move on 'business as usual' and rebuilds, goes back the way it was, whatever. I don't think this makes for much of an ending.
Chaotic Evil Ajokli wins: Creates permanent hell on Earwa, turns the remaining consult into his horseman of the apocalypse (and/or angels of death), suffering without end for all time ensues.
This is the only ending I can see with Ajokli as the absolute winner. Kind of depressing, doesn't make sense for the story as a whole, and is way to clear cut. Nothing in TSA has been so clearly "evil wins, good loses" or vise versa.
New Consult wins: This is what happened. Things are left in flux. Its now a story about men struggling against men for human ends. The Consult now strive to shut the world against the gods. Not sure this is a bad things - the gods are all terrible, but the price is so high. The rest of humanity will strive against them. Whether they know it or not, its the choice about whether or not the cost is too high. Is the price to save humanity from eternal damnation worth damning (eternally) those who must be sacrificed? Can humanity even destroy the Consult now?
This ending is the one that happened and the one that makes sense. IMO, its the perfect ending. It fits all the plot elements, leaves things in a sort of perpetual uncertainty, and leaves open the door for more story to continue. None of the other options leave room for anything significant to happen. Kellhus winning and saving humanity is too much a fairy tale option and doesn't make any sense, and Ajoki winning flat out and turning reality into hell itself is just too depressing.
So yeah, I thought the ending was great in that it fits perfectly. No other option, either above or presented by anyone else, makes any sense given the story we have.
On that note, whether Bakker never publishes another book again or if he writes a whole book every year until he dies, I don't think there will be any more 'conclusion' than what we have here. This is how Earwa will exist, forever an unanswered, unsolvable mystery. We can get more books, more world building, more information, more plots and story lines, more striving against impossible odds, but I don't believe we will ever know the final fate of Earwa.