When a songwriter and music publisher sign a deal they decide how long that contract will last. And that publishing deal will specify the duration a music publisher will administer songs on behalf of the songwriter.
Smart musicians who have a broad understanding of music publishing will not allow a music publisher to be a copyright holder forever. Because in such a scenario the music publisher will earn money from that intellectual property until well... forever (ad infinitum).
For example, a songwriter may enter a deal with a music publisher for a number of years. And when time comes to pass, either the songwriter will renew that publishing deal or get their music publishing copyrights back.
Another way a songwriter may address an issue of a music publishing contract is to reassign their publishing rights to another music publisher. So a new music publisher will administer those publishing rights and take over from a previous music publisher.
The main reason songwriters will try to retrieve their publishing rights is because the royalty payments may not be adding up. Sometimes a songwriter may suspect a music publisher of fraud and hence sue them for messing up the music publishing contract agreement.
If an aspiring songwriter can't find a music publishing company to market and promote their songs. A viable solution is to set up a publishing company and do it themselves.
And if a songwriter is also a singer who records music, they can have a publishing company set up by a lawyer. Even a personal manager for that songwriter can set up a publishing company for them if need be.
When a music publishing company is set up by the songwriter's business manager, chances are the publishing company will also be administered by the same business manager. In return, the business manager will be paid a percentage of the earnings.
In essence, a music publishing company is basically a company that will engage with other corporations in the music business. Therefore a songwriter who wants to be a music publisher needs to allocate enough time to handle all the copyright administration.
One of the advantages of owning a music publishing company is it allows the songwriter to earn more money. Especially if they are very good at what they do since more artists will demand more songs from them.
The disadvantage of starting a music publishing company is when a songwriter has no clue about music contracts. As a result, a songwriter will be paid less. Compared to potential earnings of being signed to an experienced music publisher.
For instance, in an agreement, there might be an early end proviso that states you are to pay a predefined sum to the publisher in the measure of X-amount of euros (or dollars) so as to end the initial understanding.