The system at the very least needs a way to liberate lost coins.
Coins that stay dormant for say 100 years are divided up among all current users? Is something like that possible?
It's certainly conceivable that if at some point the community perceives it to be a problem, then a majority of bitcoin clients/miners would be patched such that coins that have been dormant for that long get added in some fair fashion to the transaction fees being collected by the miners, and open clients will move coins to new addresses randomly every few years to ensure that their coins stay active. But I don't think it's anything that needs to be worried about right now.
There is no way to do this that wouldn't break the system, and I'm not even sure that the system could be broken in this manner anyway. If a wallet.dat file is destroyed, and transactions orphaned, there is no way to use those coins ever again.
Well, not without a forced address collision, but I'm presuming that we would wish to spend those coins before the sun burns out.