I agree most people wouldn't send it back. It similar to finding a lot of money on the streets. Who would honestly report it to the police? If you don't personally know the person that lost the money, humans tend to not bother about the misfortunate of a random stranger. Personally I would probably just keep it and wait what happens. It would be very hard to contact the sender with the huge anonymitiy in crpytos.  In the end I probably would exchange half of it into Bitcoins and keep the rest.