All of the internet hasn't been up for even 50 years, it's definitely interesting to consider. I think the likeliest way would be to leave an investment fund with % widthraw rate that would allow paying a developer every few years for some maintenance or needed migrations as well as enough to pay for the administration of all of this.
Otherwise you depend on friends or family to continue to do that for free across a few generations, which is a lot to trust.
What motivation does your developer employee have to go hire another developer to continue once he is gone? Seems likely that he'd just go his whole life taking your money and keeping the website up, then let everything go down once he retires/dies.
Otherwise you depend on friends or family to continue to do that for free across a few generations, which is a lot to trust.