Jim Street asked about soloing using emulated players, rather than a GM emulator.
This has been done and you can download the PDF from here:
The way it works, in brief, is that each virtual player, has an agenda, rolled on 2d6. Each time you need the characters to make a meaningful choice you will 2d6 for each player, and then move the result one step towards their Agenda. That tells you how that player will approach the problem.
The player emulator, also known as PET [Player Emulator with Tags], has many 1d6 tables to flesh out your virtual players in more detail. You could really go down the rabbit hole building a group of very detailed virtual players.
I build a very streamlined version of the PET for use in Mothership. That was a game where the crew was vitally important to the game play. Panic is contagious in Mothership. I also had to convert it to 1d10, which Mothership reads as 0-9.
You can grab the mothership rules here.
My interest in the PET was for playtesting adventures. Having a player that could easily decide to turn on the characters, for their own gain, makes for some interesting situations, and ones that may not come up that often in real in-person playtests.
It is certainly possible to run virtual players through an entire campaign of published modules. If you love DMing but your players take you for granted, you can play without them.
Another use for the PET is for when a player cannot make a game session. I would probably have a good idea of what their basic agenda would be, so from then on you can use the PET to run the missing player in a reasonably unbiased way.