After divorcing or beheading 80% of his wives at that point, what did Henry VIII's last wife expect to happen to her?

I understand where you are coming from, but the question far oversimplifies the politics and reality facing Henry VIII during the early sixteenth century. Let's take a look at this one wife at a time.

Katherine of Aragon - This is obviously the most contentious, and is often oversimplified as Henry desiring to get rid of Katherine because she could not produce an heir. This view, while compelling in popular culture, doesn't hold up to historical scrutiny. The still standard biography of Henry is J. J. Scarisbrick's Henry VIII. In the book, Scarisbrick goes to great length to show the theological problem facing Henry over his marriage to Katherine. Katherine had been married to Henry's older brother Arthur for a few brief months. Scarisbrick maintains that Arthur and Katherine did not consummate their marriage, & another major biographer John Guy, (Henry VIII, 2014) does claim that the marriage was consummated. Which ever is actually true is not the important part. What does matter is that Henry believed that his inability to produce an heir was God's punishment for breaking divine law by marrying his brothers wife. Leviticus 18:16 and 20:21 are clear texts that forbid a man from marrying (or potentially having sex with) his brother's wife. There is a counter text in Deuteronomy (25:5) but Henry felt that the divine punishment of a lack of heir was indicative that the text of Leviticus was more important. Since Henry believed he was violating God's law, his annulment (not divorce) makes sense as his only real option.

Anne Boleyn - Boleyn is a more difficult case, because the accusations she faced seem political in nature, as charges of incest seem more like wild accusations as opposed to actual crimes. The best modern biographer of Anne Boleyn, Eric Ives, argues that the charges again Boleyn were political, but masterminded by Thomas Cromwell (Ives, Anne Boleyn (1984) pp. 358-360). G. W. Bernard, in his response to Ives, argues that Anne Boleyn was actually an adulteress (Bernard, "The Fall of Anne Boleyn", English Historical Review 1991, pp. 584-610). While much of Bernard's account is fixated on proving the adultery, a more important aspect for our purposes to to see that whether or not Boleyn had committed incest or adultery, Henry believed she had. Both Ives and Bernard indicate that Henry & Cromwell went to great lengths to discover or prove the adultery, and once Henry was convinced that she had, Boleyn's case was hopeless. It makes sense for Henry to see adultery - with his advisers and trusted friends - as treasonable and worthy of an execution. Boleyn could be completely innocent, but to Henry's mind, along with the advisers unrelated to the Howard family & Cromwell, her adultery was proven and her execution inevitable.

Jane Seymour - Not much needs to be said here, as she was the most beloved of Henry's wives. She bore the future King Edward VI, and Henry was buried by her side upon his death. She died within a two weeks of giving birth to Edward (October 1537) and Henry deeply mourned her death (Loach, Edward VI; Scarisbrick, p. 497).

Anne of Cleves - Henry's marriage to Anne of Cleves was short lived, and technically annulled. Henry had only a portrait to see what she was like, and when he saw her for the first time, instantly found her plain and distasteful. Henry said of his first meeting with her that "I am ashamed that men have so praised her as they have done, and I like her not," (Scarisbrick, p. 370). The two married in January of 1540, and annulled due to the marriage being unconsummated in July (Kelly, Matrimonial Trials of Henry VIII, pp. 270-274). Anne actually lived out the remainder of her life in relative comfort in England. Though Henry is often charged with barbarity, it is worth noting that he maintained a friendship with Anne until his death, and the two exchanged letters casually for years (Warnicke, Marrying of Anne of Cleves, p. 252).

For Catherine Howard, the historian Henry Kelly explains how she was done in by her own indiscretions. She had been previously engaged to a Francis Dereham, and had had sex with him multiple times before her marriage to Henry. Kelly argues that she continued to do so after her marriage, which is why Henry's marriage to her was annulled and she was executed (Kelly, pp. 275-278). Scarisbrick agrees with this assessment, arguing that Catherine probably found her new husband repugnant and moody. Henry was, by this time, 50 years old and fat, as his portraits of the 1540s show, while Catherine Howard was about 18 and an item of desire among the men of the Tudor court (Scarisbrick, pp. 431-433). While Anne Boleyn was possibly innocent of any wrong doing, Catherine Howard without a doubt was an adulteress, though probably a young and naive one, unaware of the personal and political consequences.

So now we come to Henry's last wife, Katherine Parr. Luckily, Katherine Parr's writings and correspondence have now all been published by Janel Mueller (2011). About a week after her marriage to Henry, she wrote her brother how God had helped Henry select her, among any other woman. She continues with, it "is, as of reason it ought to be, the greatest joy and comfort that could happen to me in this world," (Katherine Parr: Complete Works, p. 46). This is a woman happy with the choice she has made. While Catherine Howard had expressed jealousy of Henry's treatment of Anne of Cleves, Katherine Parr never mentions her. In a letter Katherine Parr wrote to Henry while he was in France reads "the want of your presence, so much beloved and desired of me," (Parr, p. 63). Henry seems returns Parr's affections, and the two were known to discuss and even debate theology with one another (Scarisbrick, p. 479). When Katherine was charged with heresy (that she held Protestant sympathies is almost beyond doubt), Henry protected her and prevented her conviction and execution (Scarisbrick, pp. 479-481).

So, where does this leave us? Katherine Parr probably expected to be treated with some respect, and kept materially well during her marriage to Henry VIII. She personally took a role in helping educate Henry's three living children (Guy, Children of Henry VIII). Katherine was almost as beloved by Henry as Jane Seymour. While we look back on Henry's relationship with his wives as barbaric, it is worth looking at how Henry saw it. He thought he broke God's law with his first wife, and his second and fifth wives had betrayed him sexually and personally. His fourth wife may have had her marriage annulled and been exiled from the court, but overall she did well for herself, even gaining enough material wealth at the end of her life to send presents abroad to family members (Warnicke, Marrying of Anne of Cleves). Katherine herself did not see Henry as a danger, but as a companion and lover. She helped raise his children, was the first woman author to publish in English in 1545, and was allowed to pursue her exploration of early Protestant faith. Katherine Parr expected to be a Queen Regent of England, and in the end, that is what she was.