I considered this, too, but if an Episode IV scenario is done, I think it'd be easiest to simply make it a push map in which the Rebels have to hold off the Imperials until the Imperial tickets run out, to simulate that if they can hold the ship long enough, Leia will be given time to get to round up R2, get to the escape pod launch chamber, record her message to Obi-Wan, and launch the escape pod. You won't need an actual R2 unit and an actual Leia, just a control point near the escape pod chamber. When the Imps reach it, the round ends and you know what happens next is they shoot Leia before R2 escapes.
It could also be a map in which the boarded ship has a chance to escape, but only if it can hold off the attackers until reinforcements arrive or something. Let's say an Imperial merchant or even a corvette carrying something valuable to the Alliance has been boarded in deep space and forced to halt her progress, on threats of destruction from the Alliance ships. The rebels board her (with the map either taking place entirely aboard the vessel or with Rebel transports in space, ready to dock at the stationary ship), but she's dispatched an SOS which has caused the Imperials to scramble. The rebels thus need to take control of and make off with the ship before Imperial authorities arrive (which will happen when the rebels' tickets run out). To take control of the vessel, they need to capture the bridge and hold it for a set length to time (to simulate the need to plot a hyperspace jump and get away). If they can do this before their tickets run out, they win. Otherwise, the Imperials arrive and the Rebel boarding party will be forced to flee before they're massacred by the Imperial reinforcements.
"One of the bitches actually gave birth while she was attacking, and her puppies joined in on the carnage."
--the awesomeness that is Boatmurdered.