The highly controversial ending to the episode, which has since been referenced and parodied many times, prompted an estimated 1,000-plus letters to series producers Gene Reynolds and Larry Gelbart, and drew ire from both CBS and 20th Century Fox.
After the production of this episode, both Stevenson and Wayne Rogers, who played the character of Trapper John McIntyre, left the series to pursue other interests; while Stevenson's departure was announced prior to and written into "Abyssinia, Henry", Rogers unexpectedly left the series during the break between Seasons Three and Four, and so his character's departure takes place off-screen in the following episode, "Welcome to Korea". These combined departures and their subsequent replacements also signaled the beginning of a major shift in focus of the M*A*S*H series as a whole.
Meanwhile, Major Margaret Houlihan (Loretta Swit) and Major Frank Burns (Larry Linville) are eagerly awaiting the upcoming transfer of command of the 4077th MASH: upon Blake's departure, Burns will become the unit commander. Henry and Radar begin to clean out the main office, sharing a sentimental moment in which Radar tells Blake of his meaning to him. As a token of appreciation and admiration, Radar gives him an inscribed Winchester cartridge; a surprised Henry returns the favor by spontaneously giving to Radar a rectal thermometer that once belonged to his father.
On the night before Henry's departure, Hawkeye Pierce (Alan Alda), Trapper McIntyre (Wayne Rogers), and Radar throw a going-away party at Rosie's Bar and Grill for him. All four inebriated, they share some pleasant memories and reminisce before Blake leaves to go to the bathroom. While Henry is gone, the others prepare a comedic ceremony, in order to "drum [Henry] out of the Army". As a part of the ceremony, the three present Henry with a brand new suit as a parting gift.
The next morning is the first with Frank Burns in charge, and he immediately starts using his "gung-ho", militarily strict, and whistle-happy attitude to assemble the company. A lack of respect from his subordinates is already evident, as an out of uniform and unshaven Hawkeye and Trapper and an outrageously dressed Corporal Klinger (Jamie Farr) show up for the assembly. As Blake leaves his tent for the last time, dressed in his new suit, he is greeted with a round of applause from the unit. Frank and Margaret give Blake a formal "ten-hut" salute. Henry, in his typical laid-back fashion, tells Frank to "lay off" and to "stuff that whistle someplace".
After saying his individual goodbyes to many of the members of the 4077th, Hawkeye whispers to Henry and convinces him to give a long kiss to Margaret, generating another rousing round of applause from the onlookers. Blake then leaves the camp, walking towards the chopper pad with Hawkeye, Trapper, Margaret, Frank, Klinger, Father Mulcahy (William Christopher), and Radar, with the rest of the camp saying farewells and singing "For He's a Jolly Good Fellow".
When the helicopter arrives, it contains a wounded soldier, which occupies Hawkeye and Trapper; they say their short goodbyes before going to care for the soldier. Beginning to board the helicopter, Henry spots an emotional Radar saluting him and pauses for a moment. He runs back to him to return the salute, hug him, and leave him with the words: "You behave yourself, or I'm gonna come back and kick your butt." Blake then boards the helicopter and leaves the 4077th.
The next scene takes place later in the O.R. and has become a defining moment in the series. As surgeons are working on wounded soldiers, a visibly shaken Radar enters and delivers the shocking news:
"I have a message. Lieutenant Colonel... Henry Blake's plane... was shot down... over the Sea of Japan. It spun in. There were no survivors."
– Corporal Radar O'Reilly
Radar leaves and the camera pans the stunned and silent hospital staff, including Trapper and a teary-eyed Hawkeye, who continue to operate on the wounded, and even Majors Burns and Houlihan, who are crying. After what was then a final commercial break, the episode closes with an "affectionate and reluctant farewell" to Henry Blake, by means of a light-hearted montage of clips from past episodes.
In order to evoke genuine emotions of shock and sadness, the final O.R. scene was kept a secret from the cast, with the exception of Alan Alda (who later served as a creative consultant for the show) until the moment of filming; only then did Gelbart hand out the last page of the script. As a result, Stevenson was still on the set to see the final scene being filmed. After shooting was completed, a season-ending cast party was planned; however, McLean Stevenson left the set almost immediately after the end of filming, and the party was canceled due to the poor mood of the cast. Stevenson would later state in an interview that he was deeply hurt that his character's death was revealed just prior, and the party was "ruined." Gelbart later said of the event, "Now I wish we could say to him, 'We didn't mean it, Mac.'
However, not all reaction to the airing was negative: on the following episode of The Carol Burnett Show, the situation was parodied when the episode opened to a studio shot of Stevenson as Blake floating on a smoking raft and shouting, "I'm OK! I'm OK!
While "Abyssinia, Henry" is well-known for the departure of McLean Stevenson from the series, it was also the final episode in which Wayne Rogers participated. During the summer 1975 break between seasons three and four, Rogers quit the series. While 20th Century Fox sued Rogers for breach of contract, the lawsuit collapsed. The character of Trapper John McIntyre was subsequently written off the series in the first episode of the next season.
As a result, when the cast returned to begin filming the series' fourth season in September 1975, there were major changes in both the makeup and the direction of the show: the more down-to-earth family man Captain B.J. Hunnicutt (Mike Farrell) had replaced Trapper John, and the regular Army Colonel Sherman Potter (Harry Morgan) had replaced Henry Blake as commander of the 4077th. Another change to the composition of the show occurred in the elevation of longtime recurring guest cast member Jamie Farr, who played Corporal Maxwell Q. Klinger, to "star" status, with his name being featured on the opening credits. Episodes following this represented a major change in focus for the show: the individual effects and psychological damages of war were explored more, often in parallel to the ending of the Vietnam War, and the Korean culture was portrayed in greater depth than previously was done, instead of focusing on a "boorish, military mindset" as before.
In general, the show began to take on a more serious tone as a seriocomic (or dramedy) series, and moved away from its status as a situation comedy. To compound and hasten along these changes, during the break between the end of the third season in March 1975 and start of the fourth in September, the South Vietnam capital of Saigon was captured by the North Vietnamese army, marking the formal end of the Vietnam War.