Below is a generalized map of the holdings of the Marcher Lords. Paths are shown, and color indicates woods or non-wooded routes and holdings. North is up, so you can see to the north and east is where Twilight would lie.
Each holding has the possibility of gaining aid from at least three other holdings should an attack occur. Paths that allow such assistance to arrive in a reasonably short time are marked. The Marches are the first line of defense against the forces of Twilight and all the people of the Khelekeska state depend on their ability to deter attack.
The Iceflow River would lie south of the eastern holdings and has a few wooden bridges. Should the marcher lords here be overwhelmed or forced out of their holdings, they will retreat over the river, destroy the bridges and hold the forces there until the relief from Khelekeska and Losastar is sent.
The holdings of Icefall and those to the west have no such natural defensive barrier but they do have the mountainous terrain to use to their advantage. Should they be overwhelmed, any survivors are meant to get word to Khelekeska and then use the mountains and woods as cover while they harry the enemy as best they can. It is thought that a large army does not maneuver well enough in this area to effectively wipe out resistance.
You will note that either fall-back plan seems a tad suicidal in the face of a possible overwhelming attack. While Khelekeska does not ask her Marcher Lords to stand and die if the situation is impossible, she does ask them to do everything in their power to delay the enemy until an effective defense can be mounted elsewhere. For if the Marcher Lords cannot do their job, then Khelekeska will not have time to respond or prepare, and the destruction of the entire state will follow.