tentative: I don't get it.
You seem to be saying that somebody might be secretly working on a longer block chain, and all their hard work will be ruined because they won't be able to replace the block chain everybody else is using non-secretly because the block chain everybody else is using might get locked in. Ummm... yeah! Don't work on longer block chains in secret.
Either that, or you're saying Satoshi might accidently lock in a shorter block chain, and most people either not noticing or not caring. Umm... no, I don't see that happening.
The block chain lock-in check is only done when new blocks are accepted. Here is what would happen if Satoshi tried to commit a block lock-in that most of the network thought was shorter:
1. Imagine everybody downloads the new client with the bad lock-in.
2. Everybody who had the longer chain before ignores the lock-in, and continues to push the longer chain.
(unless the longer chain contains a bad transaction-- the chain is checked for bad transactions on startup, see CBlock::CheckBlock)
3. Newbies who are downloading the chain for the first time will hit the lock-in code, and will be running with a shorter chain.
There will be chaos as newbies generate blocks on the shorter chain, which only other newbies will accept. "oldies" will also continue to generate on the longer chain. Transactions will get added to both chains... and the "oldies" will beat Satoshi into submission. Unless there is a legitimate bug (like the overflow bug that inspired the block chain lock-in code in the first place).
If I am misunderstanding your concerns, please speak up. The number one development priority for bitcoin is security. If you have found a problem, please email or private-message Satoshi, or post here (besides possible network denial-of-service attacks-- only email about those if you have a brilliant idea for how to prevent them...).