Cut plumbing vent in attic

The HVAC contractor cut a horizontal plumbing vent run to make room for the return air duct. My understanding is that the plumbing vent needs to keep a constant slope until it goes vertical. With the duct now in the way, will the plumbing vent need to be taken vetical before the duct?

All plumbing vents under all plumbing codes need to slope downward in all cases.

This is to assure that any condensation, rain or snow infiltration will travel downhill to drains in all cases.

NEVER should any vent in any plumbing system be kept at a constant slope unless that constant slope is downhill all the way…

Can we see a photo?

2000-2006 UPC 905.1 All vent and branch vent pipes shall be free from drops or sags and each such vent shall be level or shall be so graded and connected as to drip back by gravity to the drainage pipe it serves.

905.4 All vent pipes shall extend undiminished in size above the roof, or shall be reconnected with a soil or waste vent of proper size.

If the cut vent can be rerouted around the HVAC and be level or sloped back to the drain and remain the same size there shouldn’t be a problem.