I purchased the Season Pass along with Borderlands 2 when it first came out. Since then my Xbox-live service has ended and I don't see myself paying for more anytime soon.
Will I still be able to download the other campaigns for Borderlands 2 as long as I have an internet connection, even though I only have a silver level XBL account?
Yes, you can download in-game BL2 DLC with Xbox Live Silver. Gold just allows you to play on Xbox Live with other players. If you play single player, split screen, or system link games, silver works fine.
Do note, however, that you won't be able to enter SHiFT codes (which typically give golden keys or other goodies) without a Gold account, for whatever reason.
Yes, the ability to purchase and download DLC is not dependent on having an Xbox LIVE Gold account.
Wikipedia has a matrix available that shows you what is currently possible with a free (Silver) LIVE account, and what requires a Gold account.
Yes indeed! You just need points (or, like you, the season pass), an XBL account and an internet connection!
Check this Wikipedia link, especially the tab on the right: downloadable content is available to both silver and gold subscriptions
