I think S&S clarified the waters, rather than muddying them:
Their doctrine is nothing more than a restatement of JST, and they pointed out that the only difference between JST and Bellarmine was whether or not a SECOND DECLARATION by the Church was necessary to declare Christ had deposed the pope (while BOTH AGREED the Church would have to declare the fact of the pope’s heresy).
So the idea that a pope is deposed ipso facto for heresy without a declaration of the Church is supported by nobody.
But that novel and unsupported opinion is exactly what you are proposing (and it is obviously ruinous and incompatible for the unity of the Church to have a Protestant private interpretation by private individuals determining subjectively whether or not there is a pope.
No, S&S completely distorted the evidence. They drew the line at Apostasy, whereas any obvious blatant heresy is in the same category. They misconstrue the nature of the Church's declaration and keep referring to the Church convicting the Pope of heresy, but that cannot be done. So they screw up a lot of basic concepts and muddy how this works. What is required in addition to the heresy itself is for the Church to universally recognize it as such. In some cases, it's so obvious that there's no dispute. In other cases, the Church might be divided on the matter. In yet other cases, it might be disputed whether a certain proposition is in fact heretical. In those cases, the Church needs to make up her mind on the issue, and that's the only purpose that any declaration would or could ever serve.
In the case of a blatant heresy where it's clear that Bergoglio knows that he's in heresy but holds to it anyway, there's no need for any kind of action on the part of the Church. They can simply procede to calling a new conclave.