More than 1,000 jobs rely on the waterway, whose water supply was under threat earlier this year.
The section of the A465 between Brynmawr and Gilwern was due to open in 2018.
At least 91 people have claimed compensation due to the work on the Heads of The Valleys Road.
After years changing a five-mile stretch into a dual carriageway, its speed limit could stay.
A car trim company confirms 130 jobs are being cut as the industry awaits a post-Brexit trade deal.
