If the tour goes on Lombard street and has a stop there then you can get off. I can't remember the stopping points. But wherever they have a stopping point you can get on or off. They should have a map you can view to plan ahead. I'm pretty sure there was a stop point close to Lombard if not on Lombard street. Sorry I couldn't be more specific.
You can download the Big Bus Tours app for the map of the stops. But yes, after you finish the night tour you can just stay on the bus and they will take you back to one of the stops. And there are stops on Lombard street
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