If there was a deal like returning 10% and closing the case, which hacker would want it? After all, laundering millions of dollars will not be easy, and you will always be afraid of being caught.
If a hacker worries about legal problems from hacking and fund steal because these activities are illegal, the hacker will not do it. After hacking massive fund, then start to think about legal problems, it is not logic.
10% is a good amount and he may not have to pay taxes if he does not sell it, all he needs is to wait for several years and he will have an amount equal to approximately 30% to 50% of the stolen amount legally instead of getting 100% with the fear of being arrested.
I don't think discussing about percent of total hacked amount as bounty for hacker is not worth to discuss. As it will raise a concern that hackers will try to do as biggest hacks as possible because what they earn legally after refund will be big no matter what percent of bounty paid by the project.
Like if you are hackers with $10M, don't refund to project and go to jail. In contrast, if you are hackers with $500M, refund to that project then get a bounty reward like $50M but because it is legally, as it not supposed to be, will be fine with government. It's not logic at all.
most systems tend to give rewards for finding bugs instead of entering into negotiations with hackers that may lead to a loss of 10% of the hot wallet.
It is bug bounty and serious projects have very generous bug bounty rewards for people who find and report serious bugs which can be harmful for their platforms if bad guys exploit it.