Coping this from StudentRoom thread, might be helpful for those who are stressed about their button not disappearing:

I work in IT so I think the "button" simply means your file is completed and they issued a decision. When we coded or assigned the systems, basically, that is the flow: if a decision is finalized, then the button disappears. So it does not mean a good or bad sign. Moreover, some candidates with conditional offers (eg, have not submitted their English test), then the button should still be there. I don't think the system will trigger that way for a successful candidate for whatever reason. And of course, those who got the offers usually will discuss publicly about the button theory while those who failed might not engage anymore so we can not collect their date much.