Bills wins easily. I think if Vegetto does fuse in this saga he won't surpass Bills, because he isn't even the main threat of this saga, so it'd feel throw-away which I don't think AT wants.
Not necessarily, but even being stronger than the Super Saiyan Blues. Base Vegetto has a long way to go to get to Beerus level. The way Beerus is being portrayed I wouldn't be surprised if Zamack ended up still being weaker than Beerus.
Akira Toriyama or TOEI would simply make Beerus stronger than Vegetto, excluding Whis and other OP characters, Beerus cannot be surpassed by the likes of Goku and Vegeta, not yet anyway.
Considering SSJG = SSJ seems to have been retconned, Vegetto wouldn't be significantly stronger than Buu Arc Vegetto, so Beerus would use his weird gaze attack and end things without throwing a punch.