See my soc.history.what-if posts on Sarpi, Venice, and the Interdict Crisis:
"If Sarpi's grandest dream--of Protestant armies destroying the Papacy--was
not realistic, what might he have achieved in terms of liberating Venice
from the Papacy? His strategy during the Interdict crisis was of course
to argue that it was Venice, not the Pope, which was acting in accordance
with Catholic orthodoxy. Eventually, Paul V gave way. But suppose the
Vatican is really pig-headed and insists on continuing the Interdict
despite all the evidence that it is not working and despite the French and
Spanish efforts at a face-saving compromise? Then Venice might indeed set
up a "national" church separate from Rome, with Sarpi as its chief
theologian. In the beginning it would no doubt be "Catholic without the
Pope" but as in England it might gradually become Protestantized. Of
course unless you have a much more successful Reformation in southern
Europe, a Protestant or even quasi-Protestant Venice cannot survive unless
some *Catholic* power is willing to defend it militarily against Rome. The
most likely candidate for such a power is France."
https://groups.google.com/d/msg/soc.history.what-if/87te3kZB08w/s5EKVIXIFuoJ
"The foreign power the Venetians were most counting on was France, because
they wanted a great Catholic power on their side to show that they were not
heretics. France did make a great show of friendship with Venice, but was
also worried that the Venetians as well as the Pope might be too
intransigent. What France and the other major Catholic powers ultimately did
was to lobby for a peaceful settlement of the papal-Venetian dispute, both to
enhance their own prestige and power and to prevent a war that might get out
of control. The final compromise seems to me considerably more favorable to
Venice than to the Pope: true, the two imprisoned priests were released to
the custody of the King of France, but Vencie did not repeal the laws to
which the Vatican objected (and under which the priests had been imprisoned).
So if "Venice stood alone", in a sense so did the Pope. If he had been more
pig-headed and refused compromise, he would have been isolated with no ally
except perhaps Spain. (Spain was the only power to offer the Pope military
support, but even it did so on the assumption that a compromise would be
reached and therefore it would not have to follow through on the offer.) So if a lasting schism developed betwen Rome and the Church in Venice, and it
was really clear that the fault was on the Pope's side, I am not sure that
Venice might not get French support. For that purpose, the Venetians would
at first have to maintain that the separation was "temporary" and forced on
them by the Pope, and the Venetian Church would initially have to keep the
old Catholic theology--as indeed the Church of England largely did at first.
What I am wondering is whether as in England this could eventually develop
under Sarpi's guidance (despite his public orthodox Catholicism during the
Interdict crisis) into some form of Protestantism. Protestant ideas might
infiltate in part from the foreign Protestants whose presence (and freedom to
worship) Venice tolerated in the Republic."
https://groups.google.com/d/msg/soc.history.what-if/87te3kZB08w/0-Y_EpkP76oJ