I doubt that there will be any difference in terms of reliability.
it is necessary to clearly define the requirements and tasks in which this could make sense. Usually highlights certain things that might require a database. For example - Donation system where you need to store all transactions using an intermediate link in the form of a database.
And the fact that you start rewriting all the standard saving mechanics to databases will not change much. Unless you can get rid of delays in saves, but for this you will have to rewrite the server code pretty much, where most likely you will make even more mistakes, put on crutches and eventually everything will work worse than it was originally).
A database is the same set of files and algorithms for working with them. Nothing significantly differs from the same option, where RunUO writes directly to the file.
Post automatically merged:
Also, if you just like SQL, you can already start using it in C# by System.Linq for creating tables with the data you need.