You need to remember your password and if you can't, you can try brute-force it.
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he will only need the password when he wants to sign a transaction or extract private keys
--dumpwallet should give you output of all addresses and their encrypted private keys
check this post Re: What "--dumpwallet" do (pywallet) ...
safety note: make multiple backup copies of your wallet.dat file and always work with a copy
if he already know his wallet balance and/or addresses, most likely he will ask how to recover his bitcoin