Doubt they would extend. With that said, some of the financial analysts are saying that once it looks like they got COVID-19 under control, the economy is expected to rev back up quickly. Like, REAL quick.
If that happens right as the 2 year period is about to end, the union might find that it is in the best interest of all -the union, the contractors and most importantly, our country's economy- to provide helpers to its signatory contractors ASAP and extend the list's call-time period. No way of knowing for sure what'll happen, though.