Warning: Spoilers ahead!
Star Wars: The Bad Batch series finale resulted in the deaths of these three major characters from the show. Let's recap who died and how they met their end in the finale, "The Calvary Has Arrived."
Edmon Rampart and Nala Se
Ex-Vice Admiral Rampart gets exactly what he deserves after he follows Nala Se into the science lab and points a gun at her. Showing that he hasn't changed one bit, Rampart copies the data on Project Necromancer onto a datapad, and he blackmails Nala Se to reveal what the project is about. While Nala Se reveals some fascinating insight into the project, she's readying a thermal detonator she's holding to set off the moment she drops it. As Rampart remains a greedy scum to the end, he shoots Nala Se. She releases the explosive device, which detonates before Rampart can do anything about it. The science lab, Rampart, and Nala Se all go up in flames. Nala Se ensures that all the data on Project Necromancer and any information on Omega are destroyed so that she can live freely.
Even though it's disappointing that Rampart didn't show even a degree of improvement, it doesn't come as a surprise. Some people can't be redeemed, and Rampart is one of them. Nala Se, whatever her part may have been as a scientist on Kamino, goes out heroically as her final sacrifice is done to protect the work of her people and to protect Omega. Nala Se proved her love for Omega and did what she had to do to ensure that Omega would never suffer at the hands of the Empire again.
Dr. Royce Hemlock
As Hemlock attempts to escape in his shuttle with Omega at the end of the episode, his plans get spoiled by Hunter and Crosshair. Crosshair successfully takes down Hemlock's shuttle. In a prior scene, Hemlock put a pair of binders on him and Omega, so they were physically stuck together. Hunter encourages Crosshair to shoot at the binders. As Omega stabs Hemlock in the leg as a distraction, Crosshair overcomes his nerves and hits his target, helping to free Omega. That's when Hunter shoots Hemlock multiple times, after which he falls off the bridge and to his death. It's fair to say that Hemlock and Rampart's deaths were definitely earned.
The Bad Batch series finale is now streaming on Disney+.