It doesn't have to be an outright firing (GP never used the word 'fire'), it could be that you'll get passed over for promotion or just given maintenance work until you leave.
Being taken off a project and being replaced with someone else isn't going to look too good either way, especially not if the someone else manages to do what you said couldn't be done (you're obviously sure enough of yourself that that would never be the case).
Being taken off a project and being replaced with someone else isn't going to look too good either way, especially not if the someone else manages to do what you said couldn't be done (you're obviously sure enough of yourself that that would never be the case).