The only way to see Barry is if ending B is unlocked. To get this ending the
following two points must be done:

The Trolley: Jump out the window:
Fighting Nemesis Type B on the bridge: Jump off.
After the jump off decision, the final area of the game will take a somewhat
different path. You will have to fight off Nicholai in a chopper. It is
recommended that you bring a Magnum and Grenade Launcher (or Rocket Launcher
if it has been found). You can also choose to negotiate with him.