Would Ragnarök/Surtur even be capable of destroying the Tesseract?

Question

At the beginning of Avengers: Infinity War, after Thanos announces that he is looking for the Tesseract/Space Stone, Thor informs Thanos that the Tesseract was destroyed on Asgard when Surtur carried out Ragnarök.

Would that have been enough to destroy the Tesseract and Infinity Stone inside, or could Thanos have have just swung by after the destruction and grabbed the Stone had Loki not swiped it earlier? The only indication we have that Infinity Stones can be destroyed is with the Mind Stone, and only because Scarlet Witch's abilities are derived from it, which wouldn't be applicable to Surtur and the Space Stone.

Answer 1

I think you might have answered your question.

The only reason Wanda was able to destroy the Mind Stone was because her powers derived from it.

Surtur was the second half of a prophecy involving Asgard alone. Think of him as the most(?) powerful character within that realm alone.

Who else can we think of a similar level of power? Thor, Odin before him, and Bor before him.

Bor, father of Odin, would easily be more powerful than Odin. Even he claims that he is not capable of destroying the Aether.

Now Surtur himself only shows up when Odin isn't on Asgard anymore, meaning he also feared Odin, meaning they were equally powerful, or Odin was stronger.

Since Bor was definitely at par in terms of power with Surtur, we can safely conclude that: No, Surtur could not have destroyed the Space Stone.

Answer 2

Tesseract Yes, Space Stone inside Tesseract No. Infinity Stones should be indestructibles.

"Sire, the Aether, shall we destroy it?" "If only we could, but its power is too great. Bury it deep. Somewhere no one will ever find it." _{— Einherjar & Bor [Thor: the Dark World]}