Why isn't it 'vin' in this case?
Because "sen vi" is a prepositional part of the sentence, in which case you don't use
the accusative "-n".
question, is "Mi iras vin sen" not allowed? If so, why?
"iri" is intransitive (you don’t "go something"), it doesn’t take an object, hence there is no accusative after it
multen dankon! That makes a lot of sense
So is that a yes or no?
"Mi iras vin sen" is not correct
Why "Mi iras sen vin" not accepted ? I go without /who?/what? -> you, so you is accusative like in "Mi ŝatas vin"
Ĉu li iris al Berlino?