Nobody is going to be a sperm donor anymore because of consumer DNA testing. It's not worth the risk. Just wait until some court makes the donor pay child support.
This is a great example of the principle of unintended consequences. It's interesting to reflect on whether sperm banks contracts from decades ago give them protection from lawsuits in such cases. It is even unclear the degree 23me are protected. Both policy makers, on the the regulatory side, and lawyers doing risk management, should take a hard look at stories such as this.
I'd say it's in the best interested of the child upon turning 18 to find out the identity of the father. The biological father may well be financially well off and the child would be entitled to a share of any inheritance. At the very least the child could sue the estate to get their portion of any assets.