Obviously excommunication and declarations of people as outside of the church were very much a thing for much of history. Are there records of e.g. clergy who were deemed heretical and while they believed their doctrine was right nevertheless believed the church held the power of binding and loosing and/or that if they were denied communion even for unjust reasons it would damn them?
I'm always unclear whether people took seriously the idea that the church had this simply as something in their power, the way powerful kings can execute you even if you don't deserve it, or whether they assumed that being in the right made you safe.
Okay, this one's tough because fundamentally you're trying to get inside the heads of people who've been dead for centuries. I've been at this for close to seventeen years now, and often my own answer is, "fuck if I know."
That said, I think that the first thing to remember is that excommunication is fundamentally juridical in nature. It's generally the ultimate sanction or it's something that happens ipso facto when certain crimes are committed (latae sententiae). Why do I bring this up? Well, you're generally not going to be executed for believing something so much as you are for doing something. Remember it's not a heresy to believe something incorrect about God. God is infinite and we are finite, and as a matter of course we believe incorrect things about Him all the time. It's not even heresy to proclaim something incorrect about God and His Church if it's an honest mistake: you become a heretic when you continue to proclaim something contrary to the teachings of the Church in the face of correction.
So if I'm the priest having drinks with the deacon down at the pub -- which we probably shouldn't be doing either, according to bishops' constitutions, but no matter -- and I say, "you know, I think that the doctrine of the Trinity means that God is a three headed monster sitting on a mountain" and then the deacon says, "Um, I don't think it works that way" and then later on when the archdeacon (the bishop's official) comes into town and says, "You're wrong in what you said about the Trinity" and then I say, "Oopsie!" and then fix myself based on some remedial theology training that the archdeacon assigns me, it's no heresy.
But suppose that after my correction, I stand before my congregation next Sunday and continue to proclaim the Doctrine of the Three Headed Giant. That's the point that I'm a heretic.
This brings us round to the issue of who gets punished for heresy. People punished for heresy are punished for the actual deeds associated with heresy, whether proclaiming something heretical, building a movement, or engaging in practices that are heretical.
Now, suppose that I want to proclaim heresy. Then, the question of what I believe is going on supernaturally isn't so much the issue. Remember when I said that excommunication is juridical? Well, if I'm excommunicate, I'm kicked out of the life of the community, of which the church is a huge part. If my fellow citizens are being truly devout, then they're not going to have contact with an excommunicate. At the end of the day there are sanctions being applied to bring me into line with a very real, very earthly community.
This goes doubly for kings, princes, etc. In their case, we should remember that there's a strong relationship between a monarch and the church in that the latter supplies legitimacy to the former. One reason that everyone from the country knight to the duke to the king does this is because the Church acts as sort of a recognized "umpire" for things like legitimacy of marriage and children, but also with respect even to relations between polities. The ultimate sanction of course, was for the Church to withdraw this legitimacy, to say that the king or emperor had no right to rule. So in the end, it doesn't matter whether or not you believe in really any of the Christian religion. What matters is that you act as if it's true.
Another wrinkle here is that very often a medieval or early modern monarch is able to pretty well distinguish between the pope qua vicar of Christ and the pope qua Italian prince with his own interests as a prince. When Henry VIII was still a good son of the Church he wrote a long treatise denouncing Luther and exalting the papacy and More (!) cautioned his king that at the end of the day the pope is also one prince among many. This is why you can see late medieval kings fighting the papacy's jurisdiction while still claiming to be good sons of the Church, as with the French monarchy and the Pragmatic Sanction of Bourges (1438) and the English parliament passing the statute of praemunire (1392).
So the end result is that whether or not they believed the Church had power over their souls, medieval Catholic Christians had to acknowledge the Church's very real earthly canon-legal jurisdiction.
I banged this one out rather quickly, so I'll also tag u/WelfOnTheShelf and u/Whoosier to make sure I didn't miss anything blindingly obvious.
Sorry about the delay! It's been a weird couple of days.