Thanos could have been taken down with Thor's giant gun, according to Infinity War concept art. The God of Thunder nearly traded Stormbreaker for a gun in the last Avengers film as shown in the upcoming Marvel's Avengers: Infinity War - The Art of the Movie book. The book previously shed some light on what Steve Rogers was going to look like in the film as well, which was pretty close to how he appeared in the final cut, but with a much different suit.
Marvel's Avengers: Infinity War - The Art of the Movie shows off a number of different looks for Thor in the movie. Some are close to what we eventually saw on the big screen, while others are drastically different. For instance, there's one suit that features a lot of white coloring and what looks like some silver armor. There's some versions of the suit that are simple and others that are a lot more complex. With that being said, they definitely figured out the best look for the final version.
In addition to the different Thor suits, there's different versions of Stormbreaker, as well as a design that shows the God of Thunder with a large space gun. The design of the suit looks pretty close to what we saw in Infinity War, though the character still has the eyepatch and longer hair from what we ended up seeing. While the gun looks out of place, it actually fits in well with Thor: Ragnarok since Hela destroyed the hammer Mjolnir, leaving Thor without his powers.
Taika Waititi justified the use of guns in Thor: Ragnarok because of the loss of Mjolnir and noted that Thor was at his lowest point, something that the character overcomes in Infinity War with the help of Rocket and Groot from Guardians of the Galaxy. Though it would have fit with the previous narrative, seeing Thor with a gun would have been a little off-putting, especially now that we know how the Stormbreaker axe came to be, and how it connected the Guardians to the Avengers.
Thor will be seen in Avengers 4 next, and he might be more than a little upset that he didn't go straight for Thanos' head when he had the choice. As he delivered his revenge speech, the Mad Titan was able to snap his fingers and dust half of the universe. Just as Thor was getting his mojo back after losing nearly everything, he loses it all again. However, it's believed that he will get a second chance against Thanos to reverse the events of Infinity War. The character could even decide to use a gun this time around. For now, we'll just have to wait and see. You can check out the many different versions of the Thor suit below as well as the gun below, provided by AkaSpidey's Twitter account.
Thor concept art pic.twitter.com/wwgjVNgNL1— David ⚡️ (@akaspidey) November 2, 2018