Legendary Bird Question

I'm sure we will, otherwise future new players would never be able to get an Articuno. They will probably be much rarer than now, though (pure speculation on my part).

yes i do reckon.

but as rare raid encounters/wild encounters

also lugia should be different since its MORE legendary than the 3 birds. so i wonder if lugia will continue to be caught after whatever time. most likely still yes

as scooter said they wont lock new players out of content.
and money, money and money

Not for a while. We'll see them again after special events. But they won't be always available. They are legendaries!