Here are some options depending on the nuance you want to convey:
Literal translation:
* Vivre éternellement: This is the most literal translation, but it sounds quite formal and poetic.
* Vivre pour toujours: This is a more common expression, but it can also be interpreted as "live forever" in the sense of living a very long time.
Other options:
* Être immortel: This means "to be immortal" and implies a state of never dying.
* Vivre une vie éternelle: This translates to "live an eternal life" and is a more poetic way of saying "live forever."
* Vivre dans l'éternité: This translates to "live in eternity" and emphasizes the concept of timelessness.
Context matters:
Ultimately, the best way to say "live forever" in French depends on the context. If you are talking about a fictional character, you might use "être immortel." If you are talking about a desire to live a long and fulfilling life, you might use "vivre une vie longue et heureuse."
It's always a good idea to consider the specific context and choose the phrase that best fits the situation.