The simple answer is to look at Aaron himself. Not only did he worship other gods but he was responsible for creating a graven image that led people astray. But not only was Aaron not killed in Moses' assault but Aaron became the high priest. So, if Aaron didn't die and became high priest I'm guessing that the 3000 that died that day didn't go to hell. They were just taken "out of the game". This is a testimony to God's mercy.
This is all predicated on Abraham's covenant with God. God's covenant was "one-way", meaning that even if Abraham (or his people) failed God that God would not fail him." As Paul said to Timothy...though we are faithless He remains faithful.
Now, if Aaron absolutely rejected God, then I can't be so confident of his arrival in heaven. God won't drag anyone there who doesn't want to be there. But clearly God forgave him and gave him another chance.
On a similar note and larger scale...people often misread the teaching of the Kingdom of Heaven in the New Testament. People often assume that to not be included in the Kingdom of Heaven means someone will not go to heaven. In some cases this might be true but primarily it means that a person has not embraced the moral teaching of Jesus on earth. We too often think of the Kingdom of Heaven as a place apart from earth. But Jesus and the apostles spoke of the Kingdom of Heaven as the place on earth where people are obeying God. This might throw you for another loop but you can be a believer and not be in the Kingdom of Heaven. You can be "saved" (that is, you'll be with Jesus when you die) but not be living out the Kingdom lifestyle on earth. They are two different things just like Abraham and Moses' covenants were both different. You could be a Jew who didn't live out the Ten Commandments but you are still God's child.
I realize that these thoughts might be brand new to some. But that's just because the Kingdom has not been taught well in most evangelical churches. Nor has salvation. Salvation and the Kingdom of Heaven have been seen as being in the next life. But Jesus said that they both start now. Eternal life starts the moment you believe. We bring the kingdom of heaven to earth to the degree that we obey Jesus' teaching. But just because we fail to live out the teaching doesn't mean we'll miss out on heaven. And the opposite is true, just because we obey his teachings doesn't mean we'll make it to heaven. The Kingdom of Heaven is more than a moral code. It's a relationship defined by a moral code.
My point in bringing this up is that it equates well to living out the Ten Commandments. The better we live them out the better we represent God and bring the Kingdom of Heaven to earth. But failing to live them out doesn't send us to hell! You and I can be glad for that!
I hope I haven't only muddied the waters. But if nothing else I've pointed out that things aren't as simplistic as the church has often painted them. Let's be careful with our assumptions about hell and who goes there.