It may happen eventually, but hopefully we will have migrated to stronger crypto by then. I do wonder what will happen to abandoned coins at that point. Will they become invalid after a migration period, or will they be up for grabs to the fastest cracker?
Making them invalid would be self-defeating to bitcoin, but it's not bitcoin's fault that some day abandoned wallets will become breakable, there will never be an everlasting bullet-proof encryption, and my point is: It won't happen tomorrow, it may take tens or hundreds of years, but it will certainly happen.
Perhaps there could be a solution whereby a nLockTime'd transactions could be presented during the migration period. I haven't thought through the details.
Either way, treasure hunting in the future will almost certainly be of the digital variety.