A couple of relevant rules:
Locked in Combat, p47 wrote:Units are no longer locked in combat if, at the end of any phase, they no longer have any models in base contact with an enemy unit.
Multiple Combats - Assault Results wrote:If none of a unit's models are in base contact with any enemy models, and the combined Pile In moves would be insufficient to bring them into base contact with a unit that is locked in that close combat, it Consolidates instead.
So regardless of whether the unit of Sicarians cannot get into b2b because there is no room, or because they are too far away and cannot reach, they consolidate and are no longer locked in combat when the end of the phase is reached.