Warhammer 40,000: Space Marine was originally designed to be a trilogy, and the original ended on something of a cliffhanger. Unfortunately, scheduling conflicts and THQ's eventual bankruptcy changed those plans significantly and Captain Titus' fate will remain unexplored. With no Space Marine planned for the future, director Raphael van Lierop decided to discuss what ultimately would have happened to Space Marine's leading character.
"I had some big plans for Titus," van Lierop told Penny Arcade Report. "The second part of his story was to focus on a 'Titus Unleashed' plot--basically there were forces arrayed against him that would see his loyalty to the Adeptus Astartes pushed to its limit, and his reaction would be to kind of 'go rogue,' and we'd see a different Titus, not quite as in control as we saw him in Space Marine. He would be kicked out as a consequence--exiled, which would basically be a death sentence for him."
The Space Marine director goes on to say that Titus would have returned with a new resolve in the trilogy's final act. Other Space Marines would rally around him for one climactic conflict, and he'd become the head of a new Space Marine Chapter.
Sadly Captain Titus' return to glory may never come to be, but it's fun to wonder what might have been.