Well, of course they would hold that there are valid Masses still going on, but I doubt they believe that any existinng priests or bishops still hold the full Catholic faith.
The only one I know of that wouldn't be a heretic by their estimation, is Fr. Dominic Crawford in Minnesota who holds the same positions on EENS and NFP. Otherwise, I am unaware of any that fit their definitions.
Regardless, in their view, since "undeclared heretics" offer valid Masses (such as SSPX, Resistance, and sedevacantist groups) would mean that they do not hold the position that the Mass has ceased to exist. Given Br. Peter's love of Padre Pio, I'm sure he gives consideration to the quote attributed to the holy stigmatist that the world would sooner exist without the sun than the Mass (paraphrasing).