Dear Hiya,
Because of one misconduct, you cannot be dismissive of his tenure in your company!
Employee served for certain period in your company. In the course of his tenure, he commits a misconduct. As a punitive measure, you had suspended him. Therefore, punishment is awarded and subject matter is closed.
If employee is voluntarily separating from the company then his misconduct should not impinge this separation. Both should be seen differently. One should not have bearing on another.
Experience letters are issued to certify that the employee's tenure in your company. You can issue the certificate without any remarks also. Why would you like to mention that employee was "industrious" or not? How can you expect every employee to be industrious? Dictionary definition of "industrious" is working hard to promote an enterprise. Those who work hard might commit some commit misconduct. However, some act of misconduct cannot bring under cloud the very quality of industriousness.
Industriousness is a rare virtue. Everybody is not expected to posses it. By your logic should we construe that those who do not do any misconduct automatically become industrious? Please note that we are in 21st century and not in some Ramrajya!
Please issue the experience certificate with good remarks or at least keep it neutral. By not issuing the certificate or by mentioning negative remarks on the certificate, it could destroy his career. Destruction one's career is nothing but vindictiveness of the highest kind! Better to refrain from such fiendishness!
Thanks,
Dinesh Divekar