It's the dump valve sensing line, and looks like it's tee'd off to a boost guage. Not the clearest of pic's. You will have no dump valve operation, and the dump valve may leak boost if griving hard. The ECU should pick it up as an air leak or similar, and bring on MIL light. It's OK to drive, but don't push it hard. Make sure that the small hose is not going to a boost guage, and not the fuel pressure regulator, drive very gently if it is. Where are you based, I may have something in the workshop to sort you out.
John