What the employee has done amounts to theft certainly! It must be taken to its logical end. These are delicate matters that involve intellectual property. To be LEGALLY right in deciding the course of action against the delinquent, one will have to bear in mind, at this FORMAL level, the applicable LAW concerning this matter, the principles of Natural Justice, and only then decide within the parameters set out by these. This could be time-consuming and frustrating. The accused might even pay the demanded amount and get away with the crime. This is like a thief returning stolen property and walking away clean!
Typically, this situation calls for JUSTICE (i.e., being LEGALLY and MORALLY right!). Prima facie, efforts to be legally right will frustrate necessary action. No mundane "fine" can be an adequate response.
Personally, I am of the opinion that IF the theft is REAL and is considered objectively, then it is more than adequate to be just MORALLY right and to that extent, perhaps it will meet the ends of justice to terminate the employment of such an employee regardless of level, tenure of employment, and competence as the "crime" that he has committed is ghastly and cannot be atoned for by things like punishments whether fines or others OR forcing him to BUY the said "research paper" as this person is setting a WRONG example for everyone. Precedents apart, this crime deserves the severest response!
I am aware that a lot of people may find my response unacceptable, but over time they will agree when they break away from the conventional mold of thoughts!
Regards,
samvedan