hi? bitcoin that will lost by accident (lost private key, send to wrong address) can't be refunded, and the bitcoin will stay in that address forever, its mean that the wallet will be locked, until people input the right private key to access it, so if you say that lost bitcoin are the donation for the bitcoin holders, i think it is the wrong statement
One of the things I always think about is what happens to the lost Bitcoin will there ever get opened and will the wallet keys ever going to get a review and use to get access to the wallets.