I like the dice roll thing. The simplest would be to maybe assign a percentage of what you think the chance of rescue from friendly forces is and what the chances of being captured is and roll a couple of dice based on those percentages. Maybe have boxcars mean nobody came and you all starved to death.
Or do the wait for 10 days thing, rolling dice each day. On a 4(or something else) or less you are captured-game over. If baddies really do show, then I guess you don't need dice.
Interesting dilemma though-good luck!