Witch, wizard, warlock, mage, it's just a title [though most don't use warlock as its an insult] the thing is, while most witches/wizards follow a religious path that teaches magick, there are those who are atheist who follow witchcraft, as well as people of various faiths who cast. If you are a Christian witch, or follow a path that believes in heaven, then yes it's possible. [There is a quote in the bible against witchcraft so speak with your spiritual leader] but the majority of pagans do not believe in heaven so they wouldn't because to them there is no heaven.
No one knows for certain what happens after death, so if you worry about heaven, try some soul searching and speaking with a spiritual leader for guidance. Personally religion is personal, everyone has different views, so talk to your spiritual leader, but ultimately listen to your heart.