There are no laws which prescribe that an employee should reimburse the employer towards the visa expenses. Pursuant to your queries, it may be advised that where an employee seeks to terminate his employment contract, the employer shall not be legally entitled to receive from the employee, any amount of money against the cost of visa incurred by the employer.
Students often end up choosing a programme they are most passionate about, maybe without doing their research if that specific degree is in demand in the job market. Three or four years of sweat and perseverance, depending on their chosen field finally pays off and they enter the job market to earn an income.
What about those students in the UAE who are unable to find a job upon graduation? Because, unfortunately for them, they graduated with what is being called a "dead degree".