The solution shouldn't involve a website that requires its domain or hosting to be paid and updated every year or so because in that case, it could go offline sometime in the future just like how this forum can as OP said.
This forum does not update the domain and hosting every year. The last update is in 2019 and the expiration date is 2029 and theymos bought it for 10 years.
https://who.is/whois/bitcointalk.orgDecentralized or centralized forum, the domain must be bought by someone. You can buy it for 10 years, 50 years or 100 years if you have money for payment.