Huh, I never even thought about this! I bet Usopp would latch on with another crew, but somehow find his way back to the Straw Hats one way or another. Maybe he’d have stayed in Water 7 and become a proper shipwright in Merry’s memory?
As far as the bit about Zoro, I can’t speak for anyone but myself, but I understood him from start to finish and would not have blamed him if Usopp were left behind. Everybody involved in that falling out made their decisions consciously and with gusto, so if the long nose hadn’t come back (even if he wanted to), he’d have nobody but himself to blame. Zoro may have sounded harsh at the time, but his message was solid and completely defensible.