Re: Gallic War What If
Gaul would almost certainly not have invaded Italy.
Those who say that Caesar's victory in Gaul was anything even approaching "inevitable", I think not. The pan-Gaul alliance Vercingetorix was able to assemble came very, very close. The task Caesar set himself was an extremely difficult one. An average Roman commander could have won a battle over the Gauls. A more talented one could have one a whole string of battles, and perhaps seized permanent control of some of the Gallic lands. But Caesar was out to annex all of Gaul from the Channel to the Province, and from the Atlantic to the Rhine. The tribal nature of the Gauls that was their greatest weakness was also Caesar's greatest challenge: they were a nightmare to completely subdue. His method to success lay in extreme boldness and strategic finesse, as well as tactical genius required when the might of the legion could get him only so far in his momentous task. In the final analysis, only a general of genius would have been able to conquer Gaul completely, and afterwards only a statesman of equal genius would have been able to organize the new conquests so well that the bulk of the legions could be withdrawn to fight a Civil War, and Caesar could die and Gaul would not rise again other than a single uprising in 46 BCE that was swiftly crushed by the legions still in the country. It could be said that Caesar, unique in his combination of statemsan and military genius, was ideally suited for the job.
Back to the question at hand, if Caesar had lost at Alesia (as by all rights he should have), then that would have been that. Alesia was not a battle that there was any retreat from, and he knew that. From what we know of the man I think that he would have gone down fighting, perhaps leading his legionaries in one last, glorious charge. Had he somehow escaped, he would certainly never have retreated to the Province. He made it clear when his officers had suggested they do just that shortly before Alesia - to retreat would be to admit faliure, and that Caesar would never do. He was going to conquer Gaul or die trying.
If Caesar had perished, his legions been shattered, and the Roman presence expelled from Gaul, my personal feeling is that it would have been the end. There was a reason that no Roman general had ever ventured to try and do what Caesar did before, and having seen Caesar, acknowledged by many at this point as Rome's new foremost general, lose they would have kept their noses out. Rome without Caesar, it is likely, does not become an Empire, but more likely gradually spirals into anarchy and collapse.
As far as the Gauls are concerned, the alliance probably would not have lasted. Then again, perhaps it would have. Caesar had shown the Gauls that advantage of Nationhood. Perhaps they would have understood this and attempted to adapt. Alternatively perhaps Vercingetorix could have used the situation to achieve Averni dominance over a number of tribes. Even if things returned to normal, a precedent would have been set that the Gauls would remember if any Romans came north again.
Had Rome somehow eased itself into an Empire without Caesar, then Gaul might perhaps have been conquered, but it would have been piecemeal - one bit at a time, and would have been a long process likely never accomplished nearly to the extent Caesar managed.
My two cents on the subject of my second favorite war of the Ancient World (my favorite being the Roman Civil War that followed).