There's a ton of ways that the Bolsheviks could have avoided taking power. As others have said, absent Lenin they probably would have reunited with the Mensheviks after the February Revolution, but the biggest other option is a socialist unity government (SR-Menshevik-Bolshevik) taking power. There were a bunch of proposals to do this between the revolutions (including a proposal on the day of the October Revolution), but they failed due to strategic and ideological differences between the moderate and radical socialists. However these differences were not totally unbridgeable. In particular if the Constituent Assembly had been elected and convened prior to the October Revolution there's a good chance of some sort of socialist coalition forming.