You Can't you should have saved it whenever you knew it was there. Sorry dude :(
No. Once a Pokemon faints you can't catch him. Sorry. No. Once a Pokemon faints you can't catch him. Sorry.
No, like all legendary pokemon, if it faints, you can no longer catch it. Giratina is an exeption. If it faints in the Distortion world, you'll have one more chance to catch it in the Turnback Cave after you beat the league.
No just save it before you attack and turn it off if it faints
yes
Attempt to catch?: When you spot the Pokemon, save in the place Terrakion is and if he faints start over (Reset DSi or turn off DS and your still in the place you saved at)............... he disappears when he faints.
If you beat Dialga and Dialga faints, you can no longer catch it.
He is gone Dont try to catch him again
Yes you can! After he faints go back and he'll be there.
If Cresselia faints [same as any legendary pokemon] you cannot catch it ever unless you save before the battle and restart if you make a mistake.
I found it dificult but mespirit when he faints will just teliport to another place and for uxie and azelf you need to defeat the elite four and Cynthia then you can face them again.
You can catch Suicune at Kanto Route 25. If you run away or Suicune faints you can have a rematch at the Burned Tower.
If you battled Rayquaza and defeated it, then it's gone. You only get 1 chance to catch a legendary Pokemon.