If you are talking about platoon movement, the participants don't have to stop moving if a gap appears. They just have to close the gap.
14.22 GAPS: If an AFV is destroyed, Recalled, uses non-platoon movement (14.23) or becomes Immobile, it is no longer considered part of the platoon. A radioless AFV that suffers Recall is thereafter treated as if radio-equipped. If the remaining two AFV of a former three-AFV platoon do not fulfill the requirements of 14.21, they must move to do so at the end of the first impulse in which one or both of them enter a new hex (unless they end their MPh in their current hexes). If they haven't done so by the end of their MPh or this happens during any other phase, they immediately cease using Platoon movement.
They can only try to stop using platoon movement voluntarily at the start of their MPH-
D14.23 NON-PLATOON MOVEMENT: Radioless AFV need not set up in platoons onboard, but if at the start of its MPh such an onboard Mobile AFV is alone (i.e., doesn't meet the 14.21 requirements) or wishes to break off from its platoon (this is the only time it can do so voluntarily), it must pass a NTC in order to move during that MPh.
Human wave units don't have to move to remain contiguous. They just keep going.
25.235 ENDING THE HUMAN WAVE: A unit remains a HW Unit (even if no longer adjacent to another HW Unit) until it is: eliminated; broken; out of MF at the end of an Impulse; at the start of an Impulse in a Location (or in a hex with a pillbox) containing an armed, Known enemy unit
[EXC: if it uses the Impulse to move beneath an enemy-occupied Entrenchment counter]; or is a Guard due to capturing a SMC/Unarmed/Disrupted unit (
25.234).
