He would almost certainly be facing a new charge - of evading the prison sentence. If there is no statue of limitations for evading his prison sentence, and I suspect there isn't - he might well end up with 2 sentences.
I really don't think it would be wise for him to go to Poland again. He is bound to be on some official lists, andthen he'd have to travel on a forged passport.
Another jailable ioffence.
What was it the poet said ?
"Oh what a trangled web we weave, when first we practice to deceive " ?