You're barking up the wrong tree here. For there to have been a contingency plan there would have had to have been a plan in the first place. The entire Italian campaign appears decidedly ad hoc. Even if we take an extreme position and suppose that Caesar was expecting war in 50 he clearly did not expect war so early--Caesar did not begin to move until Jan 10, by which time he had heard that he had had war declared on him by the SCU of Jan 7. Caesar throughout the Italian campaign and considerably thereafter continued to send overtures to Pompey, and his first action in Italy was to levy three additional legions--not the stuff of a planned invasion. Moreover, Caesar's behavior in late 50 does not make sense if we suppose that at any point before Jan 10 he seriously considered an invasion. Hirtius tells us that the legions in Gaul were put into winter quarters within the province in 50, because there was worry about another revolt. This is the same reasoning behind the Law of the Ten Tribunes. One legion, the 15th, was stationed in Cisalpine Gaul, as was normal in the winter. In 50 an SC required both Pompey and Caesar to withdraw two legions to Italy for a planned Parthian campaign--Caesar sent the 15th, and Pompey sent the 1st, which he had loaned to Caesar from Spain. To replace the 15th's garrison in Cisalpine Gaul, Caesar sent the 13th, which just so happened to be the only legion anywhere nearby when word reached him of the SCU on Jan 10.

The only possible way we can get around what seems clearly to be accidental is to suppose that Caesar was planning the war all along. But then why wait for an SCU? Legitimacy wouldn't make sense--if anything, it would make Caesar seem less legitimate, since he was arguing that the consuls were overriding the senate and tribunes, and never once in the BC argues against the SCU as a legitimate form of outlawing. So what, he's baiting the senate into passing an SCU against him so that he looks like the bad guy...ok. Moreover, the SCU was something of a surprise. In the weeks leading up to Jan 7, there seemed to be no indication that a decree would be passed actually against Caesar, merely that his bid for the consulship in absentia would be denied, which is just normal professio, although it would have been in direct violation of the Law of the Ten Tribunes. Indeed, the SCU of Jan 7 came soon after the proposal that both Caesar and Pompey disband their armies together, which the senate overwhelmingly voted for. The consuls ignored the senate's vote to disarm both Caesar and Pompey and proposed an SCU on Jan 7. So that doesn't really make sense. And if Caesar was planning war all along by getting an SCU passed against him, why would he bother for months in early 49 asking Pompey to get the SCU lifted? The consensus by far is that Caesar certainly didn't expect war at that moment, if at all. I can't think of any modern scholar who says anything else...You'd be hard-pressed, actually, to find any discussion on this at all, academically. The real problem is why exactly it was so important for Caesar to secure a second consulship, that's where all the ink is spilled.