In Order of the Phoenix, when Umbridge is headmistress of Hogwarts, she is carried off into the Forbidden Forest by the Centaur herd. Later, she's in the hospital wing mute, but reacts with agitation to the sound of clip-clopping.
Professor Umbridge left Hogwarts the day before the end of term. It seemed she had crept out of the hospital wing during dinnertime, evidently hoping to depart undetected, but unfortunately for her, she met Peeves on the way, who seized his last chance to do as Fred had instructed, and chased her gleefully from the premises whacking her alternately with a walking stick and a sock full of chalk.
Order of the Phoenix - page 755 - UK Hardcover - chapter 38, The Second War Begins
Did Umbridge technically abandon her post, even though it wasn't exactly in the way Snape did? By the end of the book, Dumbledore is back as headmaster; it's unclear to me what Umbridge's status became after she was taken by the centaurs and when her title would have changed back from Headmistress to Senior Undersecretary. Dumbledore kind of reappointed himself to the position of headmaster. Did Umbridge leave Hogwarts in good standing? Based on what is known from canon, would there be a portrait of Umbridge in the headmaster's office?