I suggest to ask his any friend at office to find out the reason behind the same. Or you can dispatch a final show cause notice at his home address + email and ask him to respond within 48 hours as Employee might be going under serious circumstances and in that case you can still relieve him on a positive note considering supporting docs. Nonetheless, he should have sent a message. If he is really being unreasonable, I suggest follow your termination policy and mark him as absconding.