Eh, I won't judge you if you don't return it. If you truly need it that is, and you're not really to blame if you were to ever run with it, simply because it was an error on their part and not necessarily yours. I would probably not return it if I were in your shoes, especially if the said exchange stays silent and doesn't demand a return. If they demanded, I might give in since I'm not particularly at a difficult spot, but if they don't, I don't see a reason why I should.
Heck, you can even negotiate about retaining maybe half the amount. I'm pretty sure you have the advantage in terms of negotiation power here since you have the funds, while they don't necessarily have the right to argue due to their mistake. It's really up to your moral compass on how much you're willing to return.
It's been 4 days now, the exchange has not asked for it and the lucky guy has refused to return the money, not because the exchange has not asked for it, but because he had about 0.275 eth on the exchange and some other altcoins worth about 0.7 eth, in about 1 hour after he received the 24 eth in place of 24 usdt, the exchange emptied all his wallet, he's 0.275 eth was gone, he's altcoins worth 0.7 eth was also all gone, because of this, he decided he's not going to make contact with the exchange except they contact him which I personally don't think is possible cus they don't have any of his personal information.
After reading your first post, it's kind of hard to return the 24 Eth, although I will usually allow my conscience take over, contact the support and immediately return the money.
I believe his 0.275 Eth and altcoins worth 0.7 Eth would not have been lost if he just allowed the good Samaritan in him to do the right thing.