I agree. Of course not. In fact, to whom more is given, more will be expected.
...just as dying outside of it doesn't mean that the individual is necessarily damned.
This statement, however, conflicts with Catholic dogma, as the Church has infallibly taught that outside the Church there is no salvation.
Back to Lefebvre, though. There is also the matter of the possibility of an unjust excommunication, as they have happened before, and to canonized saints. There is the possibility of an invalid or wrongful excommunication, which never truly took place in reality or in the eyes of God let's say.
Furthermore, in the matter of Lefebvre there is the very real distinction that his was not a formal excommunication, but rather, a supposed state of pre-existing self-excommunication, latae sententiae. If he was indeed outside there Church when he died, there was no chance for him unless he had access to reunion with the Church before death, or if he wasn't really in a bad way to begin with. Both situations are quite possible.
We don't know that Lefebvre is in Hell any more than we know that John Paul II is in Heaven.
I said "I agree. Of course not. In fact, to whom more is given, more will be expected."
To clarify further, actually, yes it is a guarantee of salvation. Here's what I mean... if one is a Catholic in the state of grace, then one will be saved when they die. But one may be a Catholic not in the state of grace, in which case, what you say is correct. I assumed you meant this latter situation of course, and I'm sure we are on the same page on this point.
Since Christ gave Peter and all succeeding popes the power to bind and to loose, John Paul II's excommunication of Lefebvre was valid and just. He, like Paul VI before him, had extended the hand of reconciliation to Marcel Lefebvre more than once, only to have that ingrateful schismatic slap his hand in return. John Paul II formally excommuncated Lefebvre and the four bishops with his decree "Ecclesia Dei." Lefebvre did not merely incur an automatic excommuncation as you claim (although he may have incurred it in addition to the formal excommunication!).
As to whether or not Lefebvre is in Hell, once again only God knows. Judgment is reserved to God and there may have been mitigating factors that spared Lefebvre from damnation. All I know is that Lefebvre refused to return to the Church right up to the end of his life.