No. I interpretted the G-Man's words differerntly. Cpl. Shepard was an anomoly according to the whole plan. And while he did help in some ways, he was still in the way. He has merely been detained with no foreseeable use in mind.
I was really hoping he would show up in the future(HL2), but he didn't. The other silent warrior.
Gabe Newell dropped some fried chicken on him and killed him. How? Gabe orders the 100-pound bucket, that's how. Outraged, Gearbox detached from Valve and demanded compensation for the tragic and greasy loss of Corporal Shephard. After a drawn-out legal battle, Gearbox raked in the spoils of victory, which included, but were not limited to: Gabe Newell's personal wardrobe of single-color XXXXXL t-shirts, and all intellectual rights to the aforementioned character Adrian Shephard.
Either that, or Gearbox just moved on after licensing Unreal Engine 3. I don't remember exactly.