Struthio is probably considered an example of a dogmatic sedevacantist. Yet in another thread when I asked him what if sufficiently many years passed, he answered:
"I would (have to) admit that my current assessment of the situation is or was wrong, as soon as the generation of the Robber Council will have passed away (which cannot happen while I have to continue in this life)."
Edit: Just saw, "UDS is a logical corollary of DS." Ok. I would have thought the Dogmatic SVist would at least become non-dogmatic Svist in light of powerful evidence to the contrary. Also, a dogma can only be believed with infallible faith on the authority of the teaching Church. Otherwise, it would remain something like at most a theological conclusion only. But the Church has not ruled that Pope Francis is not the Pope. Ergo, there cannot be de fide certainty that such is the case.
An analogy would be someone writing AGAINST the Immaculate Conception the day before it was defined. He may think he has good theological arguments for the same. But if it were dogmatically defined by the Church, and he wanted to remain Catholic, he would have to say, "I retract my opinion and submit to the infallible judgment of the teaching Church".
In the same way, if it were proved, for e.g. (1) that SVism leads to EVism, and (2) EVism is heretical, a sedevacantist who intends to remain Catholic should retract what was never a dogma of faith, returning to the Authority of the Church that he thought had defected.