As long as this is a Garthanos special thread, I should be able to quote myself.
Oh, and the defender should totally be able to 'hold them off.' The defender doesn't have to be able to flee to initiate the Escape, and you can count any marked enemies as unable to take OAs, and not part of the first round of the SC. (Though exactly what the enemy 'does' in the SC I hadn't thought about... usually it's just PC actions...)
And, each round the Defender can keep enemies marked or hold a choke point or whatever, that's a success he contributes to the SC.
...then, consequences...
Failure: The encounter resumes in a new location. Or the party gets away but blunders into a new, perhaps even more difficult (in their weakened condition) encounter. Or the party escapes but fails to meet some important goal (loses travel time in a time-important situation, loses the chance to rescue an npc or retrieve an item, etc).
Success: Whole party escapes, if someone was 'holding them off,' he either got away, or the enemy eventually left him behind (for dead, if dropped) to chase after the party, so he re-joins them later. They get clean away, they only encounter those enemies again if they go looking for them, or return to an area they're guarding.
One failure: The party escapes but the enemy is still tracking them and could show up again at some point in the future. Or one ally who failed (or the defender 'holding them off') is captured or separated from the rest of the party for a time. Or, the party escapes but the failure gives the enemy a round of unanswered ranged attacks against them.
Two Failures: The party gets in a short rest before the enemy catches up to them. Or most of the party escape but some are captured or separated from them for a time. Or the party escapes, but faces a different (possibly easier or less hostile) encounter they blunder into in their flight.