Let me clarify by saying that, it is not my own opinion that he should have kept going or that he needed to continue the wars. My comment above is instead suggesting what he felt he had to do.

Ceasar was in a hole of his own doing. This tends to be the case with those who push their luck with war, walls start coming in from all sides and leaving Gaul certainly wouldn't just stop the conflict he had begun. My point above was simply suggesting that Ceasar FELT he needed conclude the war, leaving no ghosts to haunt him.

Aas /r/PDV87 noted below, Ceasar was in many ways running on bought time. He was already operating far out of regular roman juristiction and who knows what he actually felt about being in Gaul--perhaps he felt it was not safe to return to Rome until he had settled what he had started in Gaul.

It had in many ways become his war, and that is reflected in his rejection of adhering to the senate.