If Caesar dies in Gaul, Pompey would need to get by without the help of his support and that of the late Crassus. The Boni faction largely disliked Pompey. He wasn't simply a "Novus Homo", he had inherited the command of three legions from his father as a young man, long before he ever formally beacme a Senator. Quite unheard of. For them, Pompey always got what he wanted by force at arms, plus, he had once done the murderous bidding of the Dictator Lucius Cornelius Sulla. With Caesar gone, Pompey would have to retain command of his own private army, and thus his remain as the unofficial power above the Senate. How long would his traditionalist peers tolerate him?
Gaul might be attacked again by someone with the same drive as Caesar. But keep in mind that Dacia itself wasn't conquered by Rome until the early Second Century CE. And Dacian society was not only sophisticated, with their own road system, running water, state religion, and iron-working industries, but also like Gaul, had extensive goldmines as well. Apparently, as Caesar was made Proconsul of Cisalpine and Transalpine Gaul, he was also the governor of Illyria, and was said to have initially planned to invade Dacia. But he felt that campaigning in Gaul had more to offer his political career.