I don't know what would happen initially, but eventually, the contractors wise up and start baking the risk of delays into their quotes.
Contractors will be extreme sticklers about their requirements on a project. So that if anything starts look off-plan or may impact something like a schedule delay they will say "nope, that's outside of our scope of work we need an extension/additional funding".
Yup, change orders are how deal with these issues when it comes to fixed-costs contacts. For better or worse, its almost impossible for a project to be perfectly specced out ahead of time. And anything that even comes close to looking like it conflicts with the spec becomes a change order.
> About that “plague”: NASA has traditionally procured technology from industry using cost-plus contracts, which allow contractors to charge the agency extra for extensions and changes to their plans.
From my experience, the author of that article has no idea what they are talking about.