The rules may change for international, but I've been proactively VDB/reroute on another airline as well as asked if I'd be interested in a proactive VDB/OAL reroute in a handful of cases [once declined because the only available option was DL, and in August of 2004 I swore I'd never set foot on DL again, in another because I was planning on meeting a distant friend for lunch in ORD while our paths briefly crossed].

Actually last week in MOT the GAs were offering $400 and "any airline from any airport" for someone willing to give up a seat starting from when they showed up at the gate at T-60 (they were -2 with a weight restriction, and at/over for the rest of the day, Delta's flights were all -10 or more from what I overhead)

The real answer may depend on how "desperate" the situation is looking -- -1, eh...odds are it will sort itself out, -10 someone is probably going to have to figure something out.