Sorry to hear about your situation. I'd suggest you keep talking to him when it seems right to do so, even if he's not responding. Assume he can hear you. Don't feel guilty if you're not there at the final moment - you need rest, and must conserve some strength for all that follows. Five weeks ago my step dad was given a few days to live, and he went within two days - get any close relatives to visit now, without delay. His brother didn't arrive on time to see him before he died.