Thursday's first practice lasted only eight minutes before Sainz's car hit the metal cover in a storm of sparks. The second session eventually started at 2:30 A.M. local time on Friday after safety checks.
Race stewards turned down the team's request for penalty-free repairs because they said they were obliged to apply the regulations as written.
"The stewards note that if they had the authority to grant a derogation in what they consider in this case to be mitigating, unusual and unfortunate circumstances, they would have done so," they said.
"However the regulations do not allow such action."
The Ferrari's survival cell, engine, energy store and control electronics were all damaged beyond repair.
Drivers are allowed two energy stores for the season and Sainz will now be on his third, triggering an automatic 10-place penalty.
Sainz took part in second practice, finishing second fastest behind team mate Charles Leclerc, and he hailed his mechanics for a "heroic" effort.
The joy at getting back on track then evaporated when the team told him of the penalty.
"I was quite excited and optimistic," he told reporters.
"Unfortunately as the session finished the team told me I was taking a 10 place grid penalty for something that I and the team have no fault and obviously this has changed completely my mindset and my opinion on the weekend and how the weekend is going to go from now on.
"You will not see me very happy this weekend," he added.
Sainz said there would be overtaking opportunities but he was too upset to discuss what might happen.
"What happened today for me is a very clear example of how this sport can be improved in so many ways," he said.
"The FIA, teams, rules -- this could clearly be applied as force majeure for me not to take a penalty but some way there's always people, always ways to make the situation worse for an individual and I think in this case it's my turn to pay the price."
Ferrari boss Fred Vasseur said the incident was "unacceptable".
"I think it's tough for a team to arrive in Vegas and to have this kind of incident," he said.
Vasseur told reporters after first practice that the incident would cost his team a fortune.
"For sure I'm frustrated. I'm also scared because Carlos hit a metallic part at 320 kph and it could have been much worse," Vasseur said.
McLaren boss Zak Brown sympathised with Ferrari and said he would have supported a waiver.
"You've got to say that's force majeure, that's nothing of their own doing," he told Sky Sports. "A very unfortunate and unique incident. I was a bit surprised to see that.
"I think we need to be a bit more supporting if something like that happens. I would support them not getting a penalty."