Very intruiging question. You are refering to the following part of the rules
Quote:
1.13.2 Becoming Broken
Check to see if a formation is broken after it receives any Blast markers (either from failing an Action test, shooting or winning an assault). Formations that lose an assault are automatically broken. You should completely resolve an assault or an attacking formation’s shooting before checking to see if the target formation breaks (ie, don’t break a formation that comes under fire until all of the shooting has been resolved).
The other relevant part is an extension of section 1.3 Blast Markers quoted by Zombo
Quote:
• In addition, a formation receives one Blast marker every time a unit is destroyed, unless the rules specifically state otherwise.
• Each Blast marker suppresses one unit in the formation and stops it from shooting. Blast markers also affect a
formation’s ability to carry out actions, win assaults, and rally. A formation is broken when the number of Blast
markers equals the number of units in the formation, unless the rules specifically state otherwise. A broken formation has to withdraw, and is not allowed to take actions in the action phase (which basically means it can’t move or shoot). It must try to rally in the end phase.
As Zombo says, the rules suggest that hits caused this way are not excluded from receiving BMs, and it seems that it gained enough to potentially break it.
In this case, while 1.3 states that a formation breaks when the BMS match or exceed the number of units, 1.13.2 gives the timing of when the formation breaks. RAW, the formation did not win or lose the assault (which in any event has not yet been resolved), but it also has not suffered from shooting either. So I would tentatively suggest that it would actually remain 'alive' until it is shot, fails an activation or loses an assault. If so, it could still provide support fire in the situation presented.
This is a special case that only results from WE critical hits - so for example an Ork Battlefortress containing a lot of Orks doubles through dangerous terrain at high speed, assuming that it might take limited damage. Unfortunately it does take damage that goes critical, destroying the Battlefortress. The transported formation tests, losing many units. If you follow this logic, the formation remnants would attempt to rally in the end phase before trying to activate in the following turn. If it passes (the formation would presumably be trying to Marshall) it might just remove sufficient BMs to become viable again.
