A couple of questions please

a) Does the banner character retain its own icons and strength when attached to another character

b) Does the banner character get killed / discarded when the attached character gets killed, discarded, (or returned to of deck due to Stalwart)

thanks in advance

Daenarys said:

a) no, it becomes an attachment for all intents and purposes

b) the banner attachment is discarded when the attached character leaves play for any reason

The short answer to both of these questions is that the Banner character becomes an attachment - and only an attachment - so is treated the same as any other attachment would be.

So while it technically "retains" its STR and icons, you can't do anything with that STR and icons because there is absolutely nothing in the game that refers to the STR or icons of attachments . Similarly, you do with the Banner the exact same thing you do with any other attachment when the card it is attached to leaves play.