If it's under factory warranty then everything inside the engine is covered under warranty.This exact thing just happened to me Saturday night while driving home at 80 kms.
The rpms dropped and the truck slowed right down. I had to pull off the road quickly. Once it stopped I tried to restart it and only heard a click. And the dash said 'battery saving mode'.
The dealer just called me today to say they believe the engine is seized as they can't turn it over at all. And it will cost upto $10'000 to fix once they remove the engine, if something is broken in there that's not covered by warranty. . So I have to make a decision whether or not to go ahead and open the engine! So I'm Sol.. Out a truck, cuz I can't afford 10 grand to fix it! And I can't risk it if there's a chance it's not covered by warranty.. 😪
The battery saver mode message at the same time is suspicious. An engine failure will not cause that message. An electrical issue will. I'd get a second opinion. Techs don't make money on simple fixes. My guess is that they see an opertunity to make money and they think you look like a sucker. I don't know what your milage is but unless you modified it it's probably covered.