Bug or Feature: For the purposes of Conqueror units, being in a state of war with Indies allows them to persist. Example: England destroyed Celts, was not at war with another major civ, units remained. I waited a few turns, then WB forced peace with Indies and units all vanished. This seems to present two problems: 1) As long as they're close enough to maintain contact, AI rarely enters a state of peace with both Indy civs, which would of course allow them to keep Conq units for far long then intended if not indefinitely. 2) If this is changed to exclude Indies, cases in which the Conqueror war routinely ends with the defender's sudden destruction (mainly New World), freshly acquired cities will be left defenseless. Takeaway: perhaps the implementation can make an allowance for City Defenders to remain, however that might be dialed-in.
PS I love this idea in principal.
EDIT: Ok so it seems that Expansion armies operate differently from Scripted/Triggered ones? Ottomans were still at war with Indies, but I observed their units suddenly vanish. I was able to confirm this correlated with the expiration of their Expansion areas. I reloaded and put Ottos at war with Italy, and sure enough they kept units past expiration date. Either way I'm starting to see visions of big trouble ahead, mainly for the AI. So far as things seem to stand, a less scrupulous player can game this mechanic by maintaining a state of war with any major civ. In any case, as currently implemented (and I recognize the change is literally a few hours old), the disbandment conditions are subject to a degree of randomness (for AI anyway) that, I'd presume, betrays their intent. Fortunately it would just be a matter of tacking on a few more operations or whatever you ProgramLordz do, nay?