
This was cut on the basis that no-one would ever import a save with just one of them and it would complicate future plots. Both characters can be modded into later missions (including the endgame at the Citadel), but they can't both be imported into the sequel, as the game locks up when the player meets them at Horizon.
At one point in the original game's development, it was planned (and uncovered, via a file in the PC version) that the player could save Ashley and Kaidan during the Virmire mission, with both of them commenting in a cutscene afterwards about a "stunt" Shepard pulled to get them out safely. Castelon was ultimately cut due to a lack of time, and most of the assets intended for the planet was repurposed for the Bring Down the Sky DLC. The planet Therum is called Caleston in the beta, and rather than searching for Liara as in the final version Shepard and his squad were instead to rescue a colony of miners. Notably, however, it also gave the player the ability to play as your squadmates (and make Shepard a computer-controlled ally), and the combat interface was much more intricate and involved than what eventually appeared in the final version. The beta version of the game featured a number of elements that were not included in the final product, including a different default character model for the male Shepard (before they brought Mark Vanderloo on to provide the face-capture model), a different voice actress for Ashley, different default armor for Garrus (who also does not wear a visor over his left eye in this version) and a completely different Galaxy Map. Now head into the long corridor and finish off the marauders there. Now by this time, the ravager would have shuffled slowly to arrive at this area. When the banshee finally reaches Shepard, her health would be low enough to wipe out completely. Wait for the banshee to arrive in this area, and use all the powers (Shepard's incinerate, Edi's incinerate and Liara's Warp) on the banshee, followed by Shepard's Black Widow V on the banshee. Instead, past the door into this combat area, position Shepard, Edi and Liara near the door. To defeat these enemies, do not head into the long corridor. The lower areas of the long corridor is split into two and are occupied by a banshee and a ravager. The first difficult part of the mission comes in the form of a long corridor with a higher platform occupied by marauders. Enter this area, and finish off some pesky husks. Activate the control to drain the water, and head downstairs into the cerberus indoctrination research facility. Go past this, and find a massive indoor pool of water. Locate and view the first Miranda Lawson video terminal. Search this area thoroughly and then go downstairs and finish off some cerberus operatives.