If Anne had given birth to a healthy son she would not have been vulnerable. Her problem was that having challenged Catherine and won, she proved it could be done.

Henry could never understand why Anne didn't behave as a queen and ignore his 'flirtations'. Anne was intelligent enough to realise that her position was always open to challenge, particularly as many people didn't think she was the rightful queen. While Catherine of Aragon lived Anne was relatively safe because if Henry had decided to discard her the pressure to go back to Catherine would have been immense. Once Catherine died and Anne fell out with Cromwell over how the funds from the dissolved monasteries should be used she was vulnerable.

It's difficult to know what would have happened with Jane.  When I was researching my novel I found her the most difficult of Henry's queens to get a handle on. I suspect she wouldn't have fallen out with Cromwell so she wouldn't have been open to the political putsch that brought Anne down. I suspect she was very careful not to offend Henry so he might have accepted he was destined to father only girls. On the other hand, eight days after their wedding he met two attractive women and was lamenting his haste in remarrying so maybe she would have been discarded. I wonder whether she had the intelligence to seize the opportunity in the way Anne of Cleves did?

I think that Jane would have jumped at the chance at retiring to a convent given Henry's previous behaviour…