Jesus gave his apostles and then disciples the judgment power- what you bind here on earth is bound in heaven, etc. Also, just "believing" in Jesus isn't salvation- in English, the translation has been stuffed to "believe," which is passive, when it's actually follow, or be a follower of, which is active. Rabbis had students (discipula) who actively followed and served. We've got generations of people who want to believe they've been "saved" and that covers everything; these people mock "Catholic guilt" and you can come to your own conclusions why, rock band mega churches notwithstanding. Meanwhile, the sacrament instituted by Christ of repentance and forgiveness is always followed by 'go forth and sin no more,' when it's painfully obvious we humans are weak and transgress repeatedly. We thus come back to wash our garments clean again in the Blood of the Lamb through confession and penance and the sacrament of the Mass (Last Supper, communion of bread/body, etc.)

If passive belief in Christ the Son of God were enough, well, gosh, even satanists would be "saved" too! They believe, right? They just really HATE. Absurd but that's what logically extends from the "I've been saved and forgiven everything" line.

Now we do not know exactly what was inside Judas, but if he was a thieving greedy man who sought political power despite knowing Jesus was the Messiah, well, that sounds hellacious. If he truly didn't recognize Jesus, then he wasn't going to be saved to heaven regardless, and might have ended up like that infamous fig tree. If he believed and somehow thought that getting Jesus arrested would force a confrontation where Jesus would mystically convince and convert the Sanhedrin, Romans and all involved, well he was still not understanding Him, and totally working against Scripture and Jesus' own teachings. But that last option would be more like mortal stupidity with arrogant manipulation (knowing better than CHRIST?), and there could be an argument made for potential eventual salvation after a VERY long penance (purgatory).

I'm sure that if it were really important for our own salvation, God would have communicated it to us all.