Jaime and Bronn rallied the troops as best they could — with no small amount of help from Dickon Tarly — but their army was completely overwhelmed.
If Jaime is dead, he at least got to go out in one of the most epic battle sequences Game of Thrones has ever produced.
He and the rest of the Lannister army found themselves facing a horde of Dothraki screamers and a gigantic black dragon that was breathing fire everywhere and on everything.
The Lannisters were taken completely by surprise as they faced a creature that should have been extinct along with an army the likes of which had never attacked on Westerosi soil.