When the expedition entered the California Nebula, events proceeded as detailed in the book, with the team hitting Toreel (they stopped calling in Lawrence once they knew it's proper name), then visiting the system of the Star Empire and the People's Rebellion, though that system was much larger than the report they sent back, having hundreds of stellar bodies, and multiple suns and protostars. After their brief time dodging Star Empire plasma fire, the group moved on to Syberia system, where they found the autonomous robotic drones warring with each other over the system, but still no sign of Manei Domini presence. From Syberia, the expedition traveled further into the nebula and encountered the world claiming to be 'Earth' which after several encounters, the expedition decided to avoid entirely.
By this time they were discovering that they HPG signals weren't leaving the nebula. Concerned, they dropped all survey tasks, and bent the whole force (or as much as was able) to the task or getting a message out of the nebula. During the course of this endeavor they also discovered that nothing could leave. Eventually they succeeded at getting a signal out in 3089, delivering the report you can download free here:
http://www.drivethrurpg.com/product/146982/BattleTech-Welcome-to-the-Nebula-CaliforniaWith some corruption entering the data (names and dates, and the full extent of the Star Empire's system) being unavoidable, they also attempted to send the information necessary to contact the expedition back. This included all of their research on the phenomena causing the interference, and their current theories, along with what they had to do to get the signal through at all. With the report finally sent, and no working theories about how they will ever exit the nebula, the Expedition gather together, and decided to settle on the most welcoming world they had found, Toreel, while they awaited the any reply from Interstellar Expeditions.
Back in the Inner Sphere, the CEO and Board of Directors received the report, and then also shared it with the Republic, and with Clan Diamond Shark, as per their prior agreement. It was decided that they would not be sending any further ships into the California Nebula, and that it was unlikely to be a place the Word of Blake would purposefully retreat to. For their part, the Republic began Project ARK, ordering the
RSS Necessitas to construct a data center, which would be essentially used as an Off-Site back-up of the full knowledge of mankind. Working with the successor states, and even the Clans, the project was simple, and ultimately successful, with the data being held and managed by a group that was theoretically neutral to the goings on in the Inner Sphere, since they could no longer be a part of it. Each group putting information into it was able to only access information they had entered, or that they had the access codes to. Not only did state of the art ECCM defend the facility, but much of the data was also on different networks, and there was no way to break from one network into the others. This facility was built as a space station in the Toreel system.
This also served as the best relief the Republic could offer to those trapped in the Nebula, all the information they could possibly use to make the new life that has been forced on them better. Once the facility was completed, and techniques for transmission into and out of the nebula refined, The Expedition gathered together once more to discuss their fate. The Republic crews felt abandoned, while the volunteers felt they had betrayed themselves via hubris. The explorers and scientists were the calmest, excepting their fate, and presenting theoretical models of plans for proceeding. Everyone still felt bound to stick together though, and lines between IES and RSS vessels blurred.
After a great deal of debate on the matter, the Expedition Leader delivered the following message:
"My bothers and sisters of this expedition, through these trying years when we have come to terms with being severed from all we knew, you have chosen to remain together and you have chosen to keep me as your leader. It is a humbling thing for so many great minds and hearts to turn to oneself for guidance. Now we are without a home, we are like a tribe wandering in the wilderness. This accursed nebula is full of worlds who are so far behind us technologically that some go so far as to praise us as divine messengers. So I say that we will not drift as vagabonds through the dust of space, begging for the scraps of worlds that don't even see beyond their own skies. This California Nebula is Our home now. It is the home of The Tribe. It is ours, and every one of us will stand at the apex and our home. We will unites these broken worlds and bring them back into the fold of humanity, guide them, until they too are ready to join The Tribe. Then together, we shall see if the boarders of this prison we shall make a home can still contain us!"
With that speech the newly formed 'Tribe', as they began calling themselves from that point on, began the 'liberation' of Toreel from the disparate city-states dotting that world. The citizens rose up and joined in this, overthrowing monarchies across the planet, in favor of the 'saviors from the sky', who had already demonstrated their ability to protect the citizens. It took mere weeks to subjugate the whole planet.