That reversal is not instantaneous, and by no means is it a guarantee that you'll ever get the whole amount back when overdraft fees, third-party bounced check fees, and all of the other non-monetary impacts are taken into account.
Depending on the scope of your accounts with the financial company that you're banking with it's possible that beyond your day-to-day operating funds and your mid-term savings accounts that you may also have access to your investments and other long-term stores of value. They aren't as liquid, and it would be harder for a thief to shift them into something that can be transferred out of your account, but it certainly is possible for it to happen if sales of stocks/bonds/etc. are conducted without your knowledge and then the funds are wired out.
In this particular case, yes, because banks tend to deny all liability for fraudulent transactions that result from credentials sharing, so the user is entirely liable for whatever loss that occurs.
It's a realistic concern. For example, a lot of elderly people are targeted for scams because they A.) Are often little easier to trick and B.) Tend to have more money. Comes up in the news a lot. They don't get it back.
Depending on the scope of your accounts with the financial company that you're banking with it's possible that beyond your day-to-day operating funds and your mid-term savings accounts that you may also have access to your investments and other long-term stores of value. They aren't as liquid, and it would be harder for a thief to shift them into something that can be transferred out of your account, but it certainly is possible for it to happen if sales of stocks/bonds/etc. are conducted without your knowledge and then the funds are wired out.