Yeah, that would be a pretty nice deal.
But they'd likely say that you are required to pay:

Fiat value of the amount of fiat or BTC you withdrew MINUS the fiat value your 30 coins had on the day you deposited them on the Exchange  (or maybe day you traded them to fiat, if the trade is not being rolled back)   MINUS any fiat value that was attributable to the "share" that you get back as MtGox creditor.

I don't think this case is comparable to Madoff because he was running a fund which claimed to make profits for those who deposited money. The people who withdrew from the fund would get more money than they deposited. MtGox never claimed to give profits on the deposited money, and nobody got more money because they had deposited anything to MtGox. The point of an exchange is to give away one form of value and get the same value back in another form.

Requiring depositors to pay back what they have withdrawn would be like if a bank went broke and anyone who had withdrawn money in the last 3 years would be required to pay it back. Most customers would have lots of deposits (from salary) and lots of withdrawals in 3 years, but that doesn't mean they've profited.