So this idea is taken from GW2 but further added on for ESO. In that game when your side lost control of everything a very strong Champion Guard would start a seige to try to retake your closest tower.
Im thinking in ESO something similar could happen. Lets say once you lose one of your main home keeps (excluding emperor requirment keeps) a timer starts, after X amount of time a Strong Champion Guard spawns at your mile gate and takes a squad of guards to try to take back your home keep that is lost (does not attack Emperor requirment keeps) players would join in. Lets say if the attack wipes, then after X amount of time a slightly stronger Champion Guard and squad spawns and heads out again... This could be something that really helps that outnumbered side.
Just an idea