Each spell with paradigm has the Lesson subtype. The Lesson subtype appears on instants and sorceries and has no inherent rules meaning. Other effects (such as the learn ability from the original Strixhaven release) may refer to it.

Once a spell with paradigm has resolved, it doesn't matter what happens to the card in exile. Even if the card leaves exile, the delayed triggered ability will still trigger during each of your first main phases, and the copy will still be created.

Paradigm creates a delayed triggered ability that triggers at the beginning of each of your first main phases for the rest of the game. When that ability resolves and the copy is created, you can choose not to cast the copy. In that case, the copy will cease to exist the next time state-based actions are checked. The delayed triggered ability will still trigger again at the beginning of your first main phase on your next turn regardless.