In this regard, what happens if articuno flies away let's go?
If your team is not up to the challenge or you run out of time before you defeat one of the birds, they will flee from battle and you will not be able to catch them. But if you beat the Elite Four and become the new Pokemon Champion, the escaped bird will respond in its old location, giving you more chance to catch it.
Secondly, can you catch zapdos after it flies away? If you didn't save after Zapdos fled, then you can reboot your game. I know that the legendary birds can spawn on regular routes after first encountering them, allowing you to catch multiple of them in a single save of LGPE.
Regarding this, can you get articuno to come back?
If it isn't, all you need to do is head to the home screen on your Switch and close out of Pokemon Let's Go. Reopen the game, reload your save, and retry again and again until you finally get the chance to capture a shiny Articuno. Good luck!
Do Legendaries Respawn let's go?
You are correct. Legendaries do respawn after beating the Elite Four. In addition to this, the three legendary birds can be found in de wild after you fought them on their original location. So the legendary birds can all be found more than once.
