Oh, I have to reply to this It will be the first time in our history where I know more than Presstab

When you encrypt wallet.dat, it encrypts the private keys, and any SUBSEQUENT transaction recorded by your wallet will have that flag as part of the blockchain data. I don't know that much about it, but it means that your old wallet will not work PAST the block it was encrypted at, which could lead to loss of coins. So the warning is made slightly more dire than it needs to be, but that's the gist of it.

As I understand it, if no further blocks were found OR your account broadcast no transactions, you could still restore from your old backup "wallet.dat" file. the other workaround, in the event that you did somehow lose your wallet (assuming you had not exhausted your keypool and refilled it) would be to dump the private keys from the old backup and import them into a new wallet.dat file.