Neither :) it is both archaic and one of Sapkowski's particular "creations"... in polish it reads (ill even turn on the PL keyboard for this... hehehe): Odejdź stąd i wychędoż się sam.
There's nothing particularly rude about Odejdz (though turning it into bugger is an inspired translation solution). It's a form of the verb to go, with the prefix od to give it a meaning of get away from here. Stad = here.
As for wychedoz, that is also a verb with a prefix that slightly modifies the meaning. Wy is a prefix that is very common in PL and mostly has meaning associated with exiting. W alone is same but for entering. Of course for certain rhytmic activities I'd say the difference is moot - it's just emphasis. :) Chedozyc sie is definitively understood as slang of fuck, and associated with Sapkowski and the Witcher books, previous to which it may not have been common usage. Ah, the sie is a reflexive, so it's literally not to fuck, but to fuck oneself (somewhat misleading as polish sie does not carry any singular vs plural or any specific person - I, you, we, etc).
I checked online dictionaries and it apparently has a correct meaning related to cleaning, ordering. Now, Sapkowski is a smart and creative guy, but the word did have some archaic documented appearences where the meaning is related to cohabitation and intimacy, it's just that such was not an accepted "dictionary" meaning. And it still isn't, though it is for sure slang.
And you see, here is the trouble with Sapkowski translations - much as I am not a native, but his prose is very natural and carries a lot of subtle meaning. You used the word poetic, which I would not use at least in its normally understood modes of sonority, rhythm, etc... as his prose is nothing like that, it is very natural but carrying a lot of subtle word plays and references that will be intimately related to polish language, both vulgar and literate. This gets lost in translation, and it typically falls into one of two sides - the translator uses colloquial, country style, popular language to an extreme which is not justified by the source material, or he uses poetic, archaic, obscure style which likewise is not completely faithful to the original.
All of this, and still haven't actually answered you. :) I can say that translating from ploughing, or from fucking, to polish no one would choose the verb chedozyc. The other way around the dilemma can be solved both ways, equally valid. Me I'd go with: "Go away and mess yourself up" for a literal minded expression. Or "Go away and adulterate yourself" where adulterate would be a play on adultery, not on modification. But as you see these in english lose a lot of expressive power - they have other meanings which dominate. Maybe "Bugger off and go bugger yourself."? What you think? :)
And by the way, consider the added subtelty (with Sapkowski, I'd wager money it's intentional), that the verb in the original is used by the chaplain, translating into common language the phrase we don't know, that Geralt had said in some form of memorized religious language - he thought it was some kind of exorcism. The actual original word used for fuck we don't even know - it is possible the chaplain was choosing a more polite form for something extremely vulgar. ;)
PS: Some pages forward, Yen says to a butler/chamberlain (after Geralt brings her through the portal and the Djinn escapes her) Odchedoz sie, durniu! It's the same verb, with od instead of wy for prefix. How is it translated? :)