In all games, being defeated by a legendary Pokémon does not cause it to disappear. In all games in which roaming Pokémon exist, fleeing
from them does not cause them to vanish; the game simply behaves the
same as if they were the ones to flee. In Pokémon FireRed,
LeafGreen, and Emerald, if the player flees from a stationary
legendary Pokémon it will reappear upon leaving and re-entering the
room, unlike the previous games where a stationary legendary Pokémon
could only be encountered once. The game informs the player that "The
<Pokémon> flew away!" In Pokémon Platinum, if the player defeats or
flees from a stationary legendary Pokémon, it reappears after the
player enters the Hall of Fame again. If the player defeats a roaming
Pokémon, the player must re-trigger the event which caused it to start
roaming; for example, the player must talk to Professor Oak to cause a
legendary bird to resume roaming. If the player flees from or defeats
Origin Forme Giratina in the Distortion World, it will reappear in
Turnback Cave in its Altered Forme, where it behaves in the same way
as all other stationary legendary Pokémon. This was extended to all
stationary Pokémon (red Gyarados, Sudowoodo and Snorlax) in HeartGold
and SoulSilver. If Suicune is defeated or fled from, Eusine will
comment on this fact, and it will instead reappear at the Burned
Tower, where it behaves in the same way as all other stationary
legendary Pokémon. If Ho-OhHG or LugiaSS is defeated or fled from
during the storyline, the Kimono Girls will comment on this fact then
leave, but the two still behave like all stationary Pokémon. In
Pokémon Black and White, ReshiramB or ZekromW must be caught;
defeating, fleeing or losing to the Pokémon does not cause it to
disappear, and the story cannot be progressed until it is caught;
instead, the player is warped back to the Pokémon League Pokémon
Center to try again. However, if the player has a full party and PC,
it is possible to progress without catching it. If this situation
occurs, it will instead appear at Dragonspiral Tower after defeating
Team Plasma, where it behaves in the same way as all other stationary
legendary Pokémon. However, it will still not give any experience
points even in that situation.
