Character: “Kei” For “To Go” (去) In Sichuanese
As Claw says, 去 is the historical character for it. This could come from 文白异读, that is, literary/colloquial readings. That would make sense, because colloquial readings are often either more innovative, or are a throwback.

Another option would be borrowing it from another variety, e.g. Cantonese keoi.