10 Most Believable Avengers 4 Fan Theories
2. Thanos Will Be Trapped In The Quantum Realm
The Theory
According to one theory, the fact that the Infinity Gauntlet doesn't impact Scott Lang in the Quantum Realm in Ant-Man And The Wasp suggests that they won't work there either. The Avengers will discover this and will lure Thanos into the Quantum Realm, where a bloody battle will occur and Thanos will be defeated and stranded.
The theory also suggests the Avengers will then escape and leave the Gauntlet with Thanos in the QR (after using it to get out), leaving him with a pretty but useless artefact. So it'll end up being protected from further use in the most poetic way possible.
Why It's Believable
Putting aside the last part, the idea of Thanos being trapped in the Quantum Realm is a great bit of speculation. We've already seen that the rules of the Quantum Realm are different to the "real world" thanks to Ant-Man And The Wasp and it can't have been for no reason. Marvel don't just waste plot-points.
And having Thanos trapped in the end would be rather poetic too, given that he sent his beloved daughter to her Soul World prison and also give that his dream of peace was quiet retirement on a Titan farm. Letting him live but not see that would be far better than killing him.