Lord Castleroy will die shortly after his marriage to Greer
This will leave Greer an extremely wealthy widow, which was a very powerful position for a woman to be in at the time. Leith will return from the army having distinguished himself and been rewarded for it, and Greer will be "too rich to care" about his social status compared to her own. They will marry.
- Jossed. He was caught in a protestant plot, which lead to him being imprisoned and stripped from his wealth. Greer ended up poor while Leith is caught up in a romance with the princess.
- Furthermore after being broken out of prison and going to Scotland to live. They agree to separate quietly on good terms leaving them to start up new relationships. Leith married an local pleasant girl according to Claude showing he moved on from both Greer and Claude.
Mary is Either Being Poisoned or Will Have a Miscarriage
Historically we know that Mary Stewart was fertile, as she gave birth to a son with her second husband, and later even carried twins, though she lost them to a miscarriage. Also historically speaking, the likely reason she and Francis had no children in real life was a deficiency on Francis's part. However, the show has shown that this Francis can indeed impregnate a woman. Either Mary will find herself pregnant at one point and have a miscarriage (not at all uncommon at the time), or someone has been dosing her with poison/birth control of some sort to keep her from providing an heir and stabilizing her position.
- Additionally, if Mary is being poisoned somehow to keep her from conceiving, whoever is doing it was also behind Henry's madness, as they would somehow be able to get some substance past tasters and guards into the victim.
- Confirmed, she has a miscarriage.