In her article “Why Dame Ragnell Had to Die: Feminine Usurpation of Male Authority in ‘The Wedding of Sir Gawain and Dame Ragnell,’” Mary Leech discusses how “The Wedding of Sir Gawain and Dame Ragnell” diverges significantly from other tales that make use of the Loathly Lady motif, particularly due to the fact that the ending of this variation of the tale potentially demonstrates the “tenuous nature of civilized manner and authority” (214).
Like other tales that make use of the Loathly Lady motif, “The Wedding of Sir Gawain and Dame Ragnell” discusses how women desire sovereignty over men above all else; however, Dame Ragnell displays more agency than her counterparts in other stories. Prior to her marriage, despite being an outsider, she passes the king, dresses the best, and marries whom she wants, therefore displaying agency and power. Secondly, she maintains power through her knowledge of the question. In other words, despite her hideous appearance, the knowledge makes her desirable. Dame Ragnell also retains power, after she transforms into a beautiful courtly lady by becoming such a temptress that Gawain refuses to leave her rather than go on adventures and is therefore called a coward.
Dame Ragnell’s power is in direct contrast to that Arthur’s. In addition to passing Arthur before the wedding, Arthur is portrayed as weak and ineffectual throughout due to being taken prisoner by Sir Gromer and being forced to plead for his life. He also has to rely on Gawain to marry Dam Ragnell. However, although Arthur is shown as weak, the tale lacks the didactic nature of other Loathly Lady tales: neither Arthur nor Gawain are being punished for acting discourteously or sexually assaulting a woman.
Because unlike other Loathly Ladies, Dame Ragnell is not correcting unchivalrous behavior and maintains her power once her beauty is restored—and in fact exerts even more power over Gawain—Leech argues that Dame Ragnell had to die in order to cede authority back to Arthur and to no longer subvert masculine chivalric values. While Leech is correct in her description of Dame Ragnell as a disruptive figure and interestingly notes that Dame Ragnell maintains power after her transformation, these are not necessarily the reasons that Dame Ragnell had to die. Even though after the transformation, the Loathly Lady frequently cedes some authority to the man, as in the Wife of Bath’s tale, where the fairy woman afterward “obeyed [the nameless knight] in every thing / That myghte doon hym plesance or likyng” (III.1255-56), rather than gain more power, there are other explanations. Rather, Lady Ragnell must die in order to prevent this story from contradicting other Arthurian legends because Gawain is well known as a lover, which the tale itself notes, and adventurer, not because she subverts male authority. Therefore, Dame Ragnell has to die for intertextual reasons, and due to the fact she has to die, she is able to subvert masculine authority rather than the other way around.
I agree, Nick, that while Leech made important points as to Ragnell's agency, I think that the key reason for Dame Ragnell's death (and the necessity thereof) is likely for the purpose of continuity with other Arthurian tales. Had Dame Ragnell not perished (and with Gawain in her good graces), audiences might have rejected the tale as being incongruent with other Gawain stories, the episode falling outside of the scope of belief (and desirable image of Gawain's character). With Ragnell's death, the story allowed itself to be inserted into the Gawain framework with ease and without upsetting any chronological factors.
The focus on intertextual coherency is an important one. I agree that one of the reasons that Dame Ragnell needs to die is to free the character up for his other courtly loves within the romance genre. That said, I do take pause in stating that neither Arthur nor Gawain are punished. While in Chaucer's "The Wife of Bath's Tale" the offense is overt and the knight exclaims his woe at the loathly lady's request for marriage, shame still operates throughout the court and serves as a part of that punishing factor. Arthur, as you mention, is made to look weak by Gromer Somer Jour which provides a humiliation. Additionally, he does bemoan and at least feign not telling Sir Gawain the hag's request for marriage further implicating the shame attached to such a union. It is true that Arthur's attempts to circumvent the union are frail, as has his character been up until this point, and Gawain remains an unblemished devoted and loyal knight unfazed by the request. But, Guinevere demonstrates horror at the wedding and attempts to hide it by requesting the wedding happen at night at which the loathly lady protests that it must be public in the court in front of all the other courtly ladies. Shame requires the presence and participation of other cultural participants of equal or greater status than the individual experiencing the shaming event. While Gawain's character may not express the type of shame response we see in Chaucer, that is not to say the reactions at the court are not noteworthy nor the hag who inspires them. Courtly love is a part of chivalric values, if perhaps not as important as demonstrations of prowess, so Dame Ragnell's power over Gawain is concerning since it consumes all other duties to the chivalric code. Finally, the text does imply that Arthur has acted inappropriately (not chivalric) by seizing and distributing Gromer Somer Jour's land to Gawain so, while Arthur is directly challenged for his actions, perhaps it is less surprising that it is Gawain who really takes the hit.