Even if he DID get away
bijuu take a long time to extract in the gedo, especially kyuubi
and it takes like what a year?
im sure minato or others would of stopped it by then
the BEST option was to get rid of reinforcements of KONOHA, to KEEP the bijuu, otherwise if he just ran away, he would face KONOHA eventually
to create tension between the village and the uchiha culminating in the massacre, not to mention both uchiha and the village are the biggest threat to his plans