How did you measure the performance of the employee, what was the frequency, who measured it and who validated it? Was the process transparent? Was the employee communicated at the beginning of the performance cycle on his KRAs? If he failed to attain the KRAs then did you issue him the warning letter? In the warning letter, did you write that if the performance is not improved then his services are liable for the termination?
If in spite of the issue of the warning letter, if the employee has failed to improve then you may terminate his services but on the safer side, better to conduct the domestic enquiry. The domestic enquiry should be free and fair and should not be vitiated in any way.
Lastly, apprise yourself about the legal terms like "retrenchment". Cases of separation arising out of poor performance are different from retrenchment.
Removal of an employee on account of poor performance is different from the removal on account of some misconduct. Even when an employee is removed on account of misconduct, he/she is eligible to get the salary till his/her last working day. There have to be genuine grounds for the forfeiture of the salaries and wages.
In the case at hand, you need to pay him salaries and wages till his last working day. Short payment, by any means, is illegal.
The Supreme Court has observed that misconduct on the basis of which a disciplinary action of termination from service is taken against a worker shall include any act on the part of the worker which is against the code of conduct of the establishment. Obviously, an employee is expected to perform and give results. If he does not give result or act differently, it should come under negligence or dereliction of duty. The courts will not direct the employer to keep a non performing worker. As such if you have evidences to show that the worker was given enough opportunities to improve, there is nothing wrong in terminating without paying retrenchment compensation.
However, in some other judgement,like Karnataka State Road Transport Corporation v. M. Boraiah and another, Punjab Land Development and Reclamation Corporation v. The Presiding Officer, Labour Court, Chandigarh etc the observation by the Court was different. The Court expanded the meaning of "for any reason whatsoever"in the definition of retrenchment as interpreted it as any reason other than those specifically mentioned,ie, termination on the ground of continued ill health, non renewal of contract or dismissal on the ground of misconduct.
Now we have to decide what all will come under misconduct. In my opinion all acts of an employee which deviate from the code of conduct are misconduct. An employee is expected to do a given work and if he does not do that it is dereliction of duty. As such non performance is also a misconduct. Now you have given opportunities and there are evidences to show the deviation from work. What else is required?