In reply to abr1966:
> If the exit routes are secure the foreign jihadi's should have no chance but some of the local extremists will blend in...
My guess is they will intentionally not close all the exit routes. If they leave ISIL the option of running away to Syria it will reduce their own casualties, reduce damage to Mosul and the amount of reconstruction they will need to pay for and avoid news footage of civilians getting bombed.
It is easier for the Iraqis and Americans if the final confrontation with ISIL happens in Raqua.