This is a SIM mod idea for someone else to implement.
SACUs are biologicals, why would they suicide if their ACU is dead? I suggest that a player who has lost their ACU and has SACUs does not lose the game, but this happens: The unit limit goes down to 0, but each SACU gives 200 limit (until the proper limit is reached), and the last remaining SACU is always visible to the enemy.
I think the SACU limit should be unit_limit/10. Will also make all these never-used SACU upgrades usable after reducing their cost (probably by 30%), because you won't be able to have a lot of them anyway. And no presets.