By the Immortal Gods of the Sith! Was Darth Vader being literal?

Question

In “The Final Chapter,” Marvel Comics’ adaptation of Star Wars (1977), issue no. 6, we are given the scene during the final Death Star trench run:

The film gives an abbreviated version of Darth Vader’s exclamation:

Wha—!

The comic adaptation expands his words with:

By the Immortal Gods of the Sith!

Are we to believe Darth Vader was literally appealing to the Expanded Universe “Immortal Gods of the Sith,” which the EU would later over many years prove to literally exist throughout many sources, and actually become a quite plentiful pantheon of immortal gods? Or was he just giving a Sith version of “oh crap?” Support for former might include evidence the EU Vader being a strong proponent or dogmatic adherent of Sith religious beliefs.

Answer 1

Legends

The idea of the Sith worshipping gods, immortal or otherwise, never returned during the Legends continuity, and isn't mentioned in any of the four draft scripts for the original Star Wars. The early Marvel Star Wars comics run took a lot of artistic license and introduced story elements that were later made non-canon (such as "Jabba the Hut" (sic) being a Nimbanel), so this seems to fall into the same category.

That said, Vader may have been referring to something other than gods worshipped by the Sith Order. The original Sith species worshipped several gods, and later viewed the Sith Lords as demigods, so a retcon could be imagined where he's talking about the likes of Ajunta Pall or Darth Andeddu.

Canon

It's still unclear in Canon what the "immortal gods of the Sith" are, but Vader's servant Vaneé makes reference to them while attempting to resurrect Vader in the Star Wars Adventures: Ghosts of Vader's Castle comic series. While Vaneé was a Sith acolyte, he'd also been driven insane by lava fumes, so this may or may not reflect orthodox Sith teachings.