In current builds (2.42.9e) ties to corpses are allowed and they remain after death.
I have a differnet take on the killing a multibot issue. When a biological organism dies, its cells don't all die at once. It takes damage, from outside or within. Some cells die, enough that that macro functioning of the organism is impaired beyond it's ability to repair. But other cells may live on for a long time after the macro organism is dead.
Thus, I don't see an issue with letting ties persist after death. Killing a few cells in a MB will impair it's macro function. It will be disadvantaged if it has no repair mechanims (I'm assuming the MB is more complex than the spagetti we see today) and be unable to move or hunt or whatever as well as it did. In a real sim, where selection is operating, this will probabily kill it.