Presumably people will write Wills (the same as they do now) and they could leave their wallet passwords in the Will or some similar solution. They could also simply tell their heir the wallet password on their deathbed or transfer their wallet funds to their heir before they die.
I don't think it is a problem. In 100 years tech will be so much more advanced than now. We'll have wearable computers and our wallets will probably be embedded into our wrist or something! It won't be a problem like you think it is.
Still unexpected deaths. But didn't think that through, in 100 years (if we don't destroy eachother, you never know with humans) we would probably have a new digital currency (or one besides BTC), or maybe humans would be invincible. Maybe we'll be on other planets or BTC will become useless. To many variables I didn't think about before posting.