With Tolkien you had it that he's dead long enough. If someone's over the limit that law sets for it, and as long as no-one has an acting copyright to it (seems like a copyright no-one acquirted through later purchasing), then it's something they can't do anything about.
In my country it's 70 years after an author's death it becomes like outlawed. The last one which had the copyright, it expires.
And I think you can only keep having grip of it, if you do a sequel. But in a lot of cases this surely is unprobable, either no-one is interested or it's downright unrealistic to find someone to be able to write one.

I'm not that familar with the details of the copyright, but sure you could hear a bit about it since this year Free State of Bavaria's copyright on Hitler's "Mein Kampf" expires and for that it becomes reprintable legally for the first time in Germany. Since that is a controversial book, there is talking "what to do about it to maybe keep preventing this?"