In the 5th chapter of the game Dead Space 1, you meet the Unitologist Dr. Challus Mercer for the first time in the Medical Deck.
At the end of the same chapter, you find yourself in a room equipped with a device that can be used to freeze subjects (considering it was in the Medical Deck, I suppose it was used for cryonics purpose).
The same room was filled with 5 or so tubes, each containing a frozen species of Slasher, which Dr. Mercer intended to bring back on Earth:
The work I have done must continue... will continue! I, Dr. Challus Mercer, shall serve as the catalyst to the salvation of our species! These specimens will return to Earth with me. I will spread their divine glory across the entire planet!
However, by the time you've spent aboard the Ishimura, you had plenty of time to realise how much in bad shape it was in general. There was barely any fuel left either, as stated by Hammond, after you fill it up:
Whatever you did, it's working. I have a fuel reading. It's only a quarter full, but that's enough to restore the orbit once you get the engine online.
There wasn't any space worthy craft to return on Earth either, let alone carry the necromorphs. The only shuttle that could possibly fly was the Executive one, but Kyne sabotaged it. Moreover, the ShockPoint Drive was destroyed:
I know you want to repair the Executive Shuttle and leave this place, but escape is impossible at this point. The shuttle ShockPoint Drive is destroyed. [...] At first, I lost hope. I tried to scuttle the ship, sabotage the systems.
When Hammond found it, it was missing a Singularity Core too, so it couldn't fly at all:
I think I've located a shuttle on the crew deck. The flight log says it needs a new singularity core.
Considering that anyone aboard the Ishimura was stuck there, and there's no way out (except the damaged Escape Pod #47, which Hammond jettisoned with a necromorph inside, even before we meet with the dear doctor), how did Dr. Challus Mercer intend to bring the necromorphs on Earth?