That could be a blessing in my opinion. Well honestly if that happens to me I maybe keeping them until the exchange contacted me and ask to return it but since I secured the ETH I would be asking for a compensation for returning it.
Very practical as you secured the fund then it's not that much of asking for little favor if possible. That amount of money will
let you think much deeper before deciding your next step.
Greed inside you will also matter since it's free money where decentralized network is your advantage, no way for anyone to
get it back from you without your permission.
This is why i do really have those doubts when someone do talk about on returning it because most of the time our greed will pop out and do tell that why the heck i would be returning this money?
If its been mistakenly sent out into your address then you will really find or treat it as a blessing but if you are some sort of whale that doesnt really care about 9k usd and your pride do tell you
that getting others money is bad then thats the time you will consider on giving it back but in most cases people wont surely give it back and due to being anonymous and decentralized
then theres no way that they will find out on whose the one do able to received those mistakenly sent out funds.