The line is made to the regulator and it is broken if missing. It plays no part in the working of the system. its real purpose aside from ctching spills is to vent the disphram. Thye would like the diaphram to vent with clean air so it cones from the aircleaner/pcv hose. Since its there to prevent the regulator from getting moisture and dirt and since its replacement requires a whole expensive regulator, I'd patch it or leave it as you see nevessary.
Bosch Master, ASE Master, L1
33 years MB technician