Not to gossip - but reading the reports from who saw him - it appears he died in his bed, so more likely natural causes (which I obviously hope is the case).
The time proximity to all that air travel raises speculation of a blood clot as well. If you have Factor V genetic mutation and are unaware, you can be at risk. I have a half/single mutation which is fairly common, but means using compression socks, aspirin, walking around if possible are a good idea for long travel or sedentary surgery, etc. If you have a two copies of this mutation, you would be at significant risk w/o a prescribed blood thinner during that type of travel.
He wasn't in the greatest shape, but got an amazing amount of steps in, didnt drink smoke or use drugs (apparently) and was trying to eat somewhat healthy. He was not high risk at all for sudden death at 51 w/o some kind of unknown underlying condition.