"Although making bodies and loot evaporate might be an interesting feature to think about in the future."
Truer words were rarely spoken. I think I'm now at year 4 of my fortress and the area around the entrance of my fort looks like the scene of a massacre. I've been using a dwarf-cleaner (line of water) at the front of my entrance, and running dfcleanmap multiple times per siege but it doesn't seem to help much. If there was simply a way to make bodies/bones rot quicker I think that would do the trick. It would certainly make things look neater. In any case, it's time to reset.
Also some more general comments about the mod - I've now seen multiple waves of war elephants, nightwings and warwolves, and as far as I can tell, nightwings are the worst, followed closely by the war elephants, while the warwolves are significantly weaker. The difference between nightwings and elephants is that nightwings are very hard to disable since they don't ever seem to fall unconscious even when heavily wounded, while elephants hurt alot although they are easier to bring down. At least that's what usually happens, one time I had 83 pages of combat text that was 2 axemen trying to finish off an unconscious elephant (in bronze armor IIRC). And let's not talk about the time when nightwing lashers showed up.
Probably the worst squad I faced were a bunch of nightwing axemen who served as a meatshield for their general which was a legendary +5 in spear skill with a copper spear who cut through steel like it wasn't there - I used runesmith to figure out his stats. I ran through the battle times many times by reloading and basically the general would pick off the dwarves one by one while the rest of his squad was dying slowly. I ended up reducing his stats in runesmith to proceed.