What if Caesar was killed at Alesia? There were many chances where he could have died but, for the sake of the argument, let's say he died on October 2nd. He attempts to stop Vercassivellaunos's attack and gets killed in the process, what happens next?
Well, at this stage, the romans have won Alesia. So you have a victorious roman army but its imperator is dead.
However the campaign is not over : Gaul is not wholly pacified yet. It took all the year 51 and a hard campaign to crush resistance against Rome.
The point is who will succeed Caesar.
It would be logical for Pompey to do all he can to get this new extraordinary command. Caesar was then still his political ally, and Pompey''s interest is to take back as much of Caesar's party as he can.
Because at this stage, Caesar's death means the end of what was only the beginning of a caesarian party. Even more than Crassus' death was quite disruptive and meant the end of his power and most of his followers turned to other patrons instead of remaining followers of his surviving son Marcus.
I don't expect Pompey to tolerate that Domitius Ahenobarbus obtain the gaulish command. Pompey could object to his law demanding a 5 year delay between consulship and proconsular command.
