There is no way around it, it will take substantial effort to keep Playing History viable for the future. This is a common feature for expert search style tools. The good news is that all sorts of groups already do it, including CHNM‘s History Matters. There are substantial costs, while there are strategies for off setting those costs the bottom line is that if it is useful and used it will become something worth funding and maintaining for the future.
Cost: Links break: In the ideal situation this site links to some 3000-5000 games, these links will need to be checked and updated over the entire life of the project. There are of course some tools for automatically checking them, but often sites will also change their content, requiring at least someone to check the links on an annual or bi-annual basis.
Mitigating that Cost: It might be possible to connect with a publisher to publish editions of a dead tree version, one might be able to roll the limited money related to the books into biannual refresh of the project.
Another option: As the site becomes more of a community it will be possible to involve power users from that community to contribute content. On the most basic level, giving users the ability to flag broken links would reduce the need for checking them, beyond that power users could recommend and review games they have found and used.
Unlike an archival, or web article style project. These types of projects are often concerned with preserving their projects for the ages. At least for the time being, I am not. At least initially there really wont be that much of value to save. The site will function more as a web portal, and the content is really at the end of the link after your search on someone else’s server.
With a bit of TLC it would be very reasonable to keep such a site operational for 7 years, at which point if it was successful, lets say tens or hundreds of thousands of users, it would warrant further investment to migrate to PHP 15 or whatever were up to then. If it is not successful I am sure someone will have built a better mouse trap and the world will continue to turn.