You need to give him benefit of doubt. Death of close family members in such short gap is traumatic. He might not be in a state to respond or there might not be good network in his village, his phone might have got misplaced or damaged, he might be running around with all the rituals (which really messes up the priorities when functioning in a shocked state)
You could hold back partial salary and release it when he returns.
Or you could ask him to send you the death certificates of his grandparents to enable the release of the full salary. Check the certificates on the government website for authenticity.
You terminating him in such a situation might just be a massive added blow to an already traumatised person.