Zap - I'm not an MP guy, but why not go for my friend's and I's time-honored board-game tradition when faced with certain defeat in games like Risk, etc: Sacrifice your nation in a kamikaze effort to use everything you have to take down/thwart your nemesis:
- scorched earth tactics on the territory that you're losing to him. (ie: pop killer rituals on high-pop provinces, bane venom charms on scouts, etc)
- stop fighting your other enemies, withdraw all your forces for use to fight your nemesis.
- send gold, gems, artifacts, & intelligence to any players that might also be fighting your nemesis or that have the best chance to defeat him.
The idea here is fourfold:
1) maybe you get revenge by helping take down the player that sunk you. Revenge is good.
2) the revenge motive can make a game just as or possibly even more fun/interesting than trying to win, so playing a losing game isn't such a drag.
3) These kamikaze tactics will also likely result in the game ending for you *sooner* rather than dragging on longer, so you will be free of the game without needing to go AI and disappoint anyone.
4) if in future games people know you will do this when sinking, they may not be so willing to mess with you.
win-win-win-win, IMHO.