We know who the associates of the SSPX are who have been working for the deal, and their affiliation with members of the tribe.
Germany would have broken off diplomatic relations with the Vatican?
Sounds like a total bluff to me. Just like the supposed threats to shut down the SSPX in Germany. If the German government had tried to shut down the SSPX they would have started a kulturkampf which would have radicalized some of the SSPX laity in Germany.
The SSPX would have split for sure and at least 10% of the members and Bishop Tissier would have left if there had been a deal.
That would have been a disastrous outcome for Rome, because their goal is to cook all the frogs in the same pot.
Creating a serious split would greatly reduce their control over the situation, just as the expulsion of Bishop Williamson has already reduced their control over the situation.