Sincerely, I do not know if I will return it or just keep it for my own sake. Imagine having a 100BTC to be mistakenly sent into your wallet is such a luck because there are thousands or even a million of different wallet which is uniquely different based on numbers and letter combinations and I am the one to have it. Maybe I will use it into an online casino to make some profit out on playing through its variety of games then, somehow send help to the needies to return back my luck by sharing some to them.