I think that any answer to this question warrants protection from spoilers. I would urge any prospective editors to think carefully before removing.
There is no clear answer to this and it's understandable that there may be differences of opinion. This is my take:
Elethiomel lost the war. And of course by now we know who Elethiomel is.
Here's my justification. I realise that these points are open to interpretation.
He ran away. He gave up his hostage (which appeared to be the only thing stopping an attack on the battleship).
Some quotes (from Orbit edition 2008, ISBN 978-1-85723-135-9).
Chapter VIII - p162
He tried to tell himself that, mostly, he'd won. He knew he had, but
it was only the moments of defeat, the instants of paralysis that made him
really think, and try to join up the weave of his life into a whole.
That was when his thoughts returned to the battleship Staberinde and
what it represented; that was when he thought about the Chairmaker and
the reverberating guilt behind that banal description...
It was a better sort of defeat this time, it was more impersonal.
Chapter II - p359
He ended up in another lo-tech war, learning to fly (because he knew
now that aircraft would always win against a battleship), and flying
the frosty vortices of air above the vast white islands that were the
colliding tabular icebergs.