The bitcoin will be back to around 17.5$/BTC after we rollback all trades that have happened after the huge Bitcoin sale that happened on June 20th near 3:00am (JST)....
We don't know how many people made quick transfers out of MtGox.
When they roll-back the trades, where will the missing coins come from?
Well, let's see. There's a $1000 limit. There are 60,000 accounts. I'd wager that less than half of those accounts transferred anything out. Hell, probably less than 10%. On Mt. Gox's best trading days in the millions of USD, they still only had a volume of like $30 per account, on average. Only a fraction of those 60,000 are "active users". Even less were even around to have the opportunity, as it was a holiday and a weekend.
Of those that did transfer out, several still have balances at Mt. Gox that will cover part or all of the transfer. For example, if you had $1500 and transferred $1000, after the rollback, your account will be $-500.
A small fraction of those who end up with negative accounts will pay back the transferred money. MagicalTux said they weren't going to do chargebacks, it's just that your Gox account will go negative and I assume you wouldn't be able to trade there anymore until you deposited.
However, the $1000 in transferred bitcoins after the crash could now be worth like $5k-$10k. I think I remember that the 1-cent bidder transferred 600-something bitcoins, so he's likely the maximum single account transfer value besides the hacked account.
At flat maximum based on that last point alone, then, Mt. Gox could be paying up to $600 Million for the rollback, not including whatever reconciliation they might pay to those who were screwed by the rollback.
More realistically, the average loss due to transfers was probably $200 or less per transferring account, and likely less than 3,000 accounts (5%) did a transfer covered by the rollback period that resulted in a negative account balance. That's $600k USD of losses to Mt. Gox.
Yep. That's all just wild shots in the dark, but $600k USD is 2 months of Mt Gox's cut during heavy trading. They probably have that in their profit coffers.
So that's where the missing money will come from, no need for a fractional reserve.