I think that even if he had got bored of Jane emotionally/sexually, he would have just taken a new mistress (or gone back to one of the old ones) rather than trying to have her replaced as a wife. He couldn't do away with her as a wife without it impinging on his son - not because Edward needed a mother or anything soppy like that, but to discredit her would be to discredit his heir.
Also, from 1536 onwards he seems to have become less sexually active, so I can't imagine him having a grand passion for another woman the way he had for Anne.
It might be quite stressful being Jane, though, in that you'd have the Howards and other enemies of the Seymours sniffing round all the time, and you'd know that if anything happened to Edward you'd be vulnerable.
Unless she had been able to not only stay alive but provide him with more boys, in which case she'd be fine.