At some point the fear/risk of surprise injections of coins may be enough to warrant a push to migrate to a new chain.
I cringe at the idea of invalidating old coins that haven't moved in years (think political prisoners locked up for 30yrs etc), but perhaps some mechanism could be built in to limit the rate at which old coins could be spent, based on the overall transaction volume; so that if the proportions are large there is at least some delay/warning when previously assumed destroyed coins are coming back into the economy.
Something like this will probably get implemented in the coming years. Bitcoins are not very useful for long-term storage right now anyways, because of the volatility of the price. Noone even knows if the bitcoins are going to be around for another year... I mean, cryptocurrency as a concept is not going anywhere, but what if an alternative implementation comes along that everybody will like and switch to? Contemporary clones lie ixcoin, i0coin and such are just a pathetic pump-and-dump schemes, but what if a truly innovative currency will come along?
if lost coins becomes a problem we will simply start mining them back!
If that is so simple, why don't you start mining them right now? There are plenty of lost coins out there.
Correct. Quantum computing should be capable of finding those "lost" coins by the time it becomes an issue.
Cool story, bro!