Dear Kavita,
This is a real problem, and such employees exist in most companies. Although there are policies in all companies that none of the employees should borrow money from vendors, in reality, this does not happen. Here, two important points need to be considered:
First Point
First, your company is not responsible for the personal actions and omissions of the employees, and legally, you are not responsible to the lender as the lender had not taken consent from the company before lending the money.
Second Point
The second point is when the money was given, the borrower was your employee, and he might have used his official clout to take money from the vendor's employee. The non-refund of this amount will cause an unnecessary dispute with that person. I am sure it can harm the interests of your company somewhere indirectly.
In this case, just tell the lender that your company does not appreciate these types of transactions as these transactions are treated like bribing people by vendors. Also, inform the same to his seniors. They must inform their employees strictly not to enter into similar transactions in the future, and if any of the company employees ask for some money or favors, they must inform your company immediately. You should also issue a circular to all your employees and warn them of strict action if anybody is found doing similar misconduct; he will be sacked, or strict penal action will be taken.
Resolving the Present Case
To solve the present case, assure the lender that you sympathize with him personally and will try to help him recover his dues. As your employee has left the job without intimating the company and there may be some wages or other funds payable to him, he may come to settle the accounts. Just make sure the lender is present at the time of the settlement of the account and then let them settle the account themselves.
I hope by doing so, you can settle the dispute and avoid a similar problem in the future.
Regards.