I dunno, throwing it in the river has probably brought more attention to the horrors of slavery than it sitting in some museum in Bristol would (I don't know if Bristol even has a museum tbh). You never know, it might be an incident that ends up in the history books.
I doubt the Iraqi's put that Saddam statue in a museum, or the former Soviet states with all their Stalin ones.
Not convinced museums are generally full of statues of terrible people either tbh, think that's Maddame Tussauds you're thinking of?
I agree that dragging it down isn't the "right" thing to do, but it was far more wrong that it's been allowed to stay there all these years and refusing to take it down tbh so it's the lesser evil.