Yep, it could be a great way of creating nice plausible deniability for themselves.
What a biz model:
1. Become a depositary institution (i.e. bank)
2. Accumulate lots of deposits (do not charge any meaningful fees for the service)
3. Rob yourself
4. Tell everyone that half of money gone, pay half out
Rule of thumb for punters: if someone offers to safely keep your money and do not want to charge for it, it is too good to be true.
3. Over periods of months take out small amounts at a time and sell them at high prices when no one suspects anything.
4. When first person takes BTC out that MyBitcoin can't cover then shutdown. Claim amount taken over the period to be stolen.