In the resignation the employee submits his resignation as per the terms and conditions of employment, and get himself relived from employment.
Is a process of disciplinary procedure, and principle of natural justice ( opportunity to be heard ) has to followed before his termination. In case of long absence, it is well established that, maximum opportunity to be given. Establish a documentary evidence of sending several letter, asking him to join duty, with valid explanation, to his last known address as per official records. Even you may advertise in the local news paper asking him to report for duty, with reasonable explanation and also ask him to appear for an Domestic inquiry fixed. Conduct a domestic inquiry, and document all the letters and the news paper adv as documents. Finally send a registered letter to him saying ' as you are remaining absent more than 30 days, nor do we receive any communication from your end inspire of several notices to you, and hence your services are terminated on you own volition, with a copy on the company's notice board. You may engage the services of a private detective and collect his whereabouts. Probably he may be working in some other firm or in jail after having involved some criminal / civil cases. Then thinks would be easy to terminate his service based on this, without any inquiry. You may adapt different methods, depends on the circumstances.
In case, if an employee is absconding and later we receive the resignation letter of back dated, do we have to accept his resignation with immediate effect or with the same date as given by the employee.
This treatment, will have a deterrent effect on all employees.