What role does a merger model play in deal negotiations?

The model is used as a sanity check and is used to test various assumptions. A company would never decide to do a deal based on the output of a model.

It might say, “Ok, the model tells us this deal could work and be moderately accretive – it’s worth exploring more.” 

It would never say, “Aha! This model predicts 21% accretion – we should definitely acquire them now!” 

Emotions, ego and personalities play a far bigger role in M&A (and any type of negotiation) than numbers do.