There's a six-page docuмent on the Dominicans of Avrille website, called "A refutation of sedevacantism."
http://www.dominicansavrille.us/refutation-of-sedevacantism/It doesn't cover every aspect of the debate, but it does go into detail about the issue of material vs. formal heresy. From page 2:
"1) "A heretical pope is deposed from his pontificate by the very fact of his heresy"
"To start with, it must be noted that this doctrine is not recognized as certain or even common among great theologians who dealt with this question: some think that this cannot happen, some others think that such a pope should be deposed, or forced to resign, and yet others who think that he would lose his pontificate ipso facto. Hence, it is only a probable opinion shrouded with doubts.
"Next, the word "heretic" must be understood in the moral sense. For it is in this sense that there is unanimity among theologians and canonists, that one cannot condemn someone of heresy unless it be formal (an obstinate sin, willfully denying an article of the faith defined by the Magisterium of the Church). However, it not possible for us to affirm with certainty, that of a conciliar pope, neo-modernism being just a heresy that does not directly deny defined articles of the previous Magisterium, but empties them of their substance.
"It is difficult to know if a conciliar pope is truly aware of being in formal opposition with the traditional Magisterium, especially when he speaks of the "hermeneutic of continuity." Even if that is the case objectively, it is not evident subjectively and before God that he has contracted the sin of heresy, a sin that the law of the Church requires to be declared, before being able to impute to him a crime punishable by canonical sanctions. Therein lies a new doubt. Yet, a decree of the holy office (20-07-1898 states that in case of doubt, there is presumption of material heresy.
"With the dictionary of Catholic theology (v.6 col.2221) let us add that "even feigned ignorance excuses one from the sin of formal heresy, though it does not mean that it excuses one from the sin itself."
That these conciliar popes are heretics at least materially, this is commonly agreed among us, and this is what the Superior General of the SSPX declared publically in Fideliter (No. 92, p.44) in 1993. But that they are formally, that is doubtful."