Reincarnated Inside My Own Novel ?

Will was a famous novelist of him time.
As such he wrote realistic novels (ie that had deaths, betrayal, Mc also losing etc etc).
In his most recent novel , 3 out of 4 MCs were killed by him.
But fate has something else in store for him. He has been reincarnated in his own novel.
But that's not the end. His mission ? To save the 3 MCs which were killed in his novel, and if he fails it leads to his death.
Whats even worse is that he has been reincarnated as a mob character.
How will he save the 3 MCs and in turn himself ? Let's find out