À la vie, à la mort. – Thrown grenade is a sticky proximity mine. When approached by an enemy or after a long delay, the grenade rises into the air and explodes into homing rockets.
Additionally, the grenade's legendary ability (being a sticky proximity mine) is very similar to one of Widowmaker's abilities, Venom Mine, which is a proximity mine that, when triggered, deals damage over time.
The flavor text is literally translated as "to life, to death". As a French expression, however, it is taken to mean "'til death do us part" or "united forever".