harry potter - What would happen if a muggle went inside the Diagon Alley? Assuming they could

I don´t know if the canon specifies whether a muggle can or can´t enter Diagon Alley In this question, someone asked if Diagon Alley can be accessed through the sky, and apparently it´s possible.

What would happen then if a muggle entered Diagon Alley?

Answer

Very little

There's no evidence of anything preventing Muggles from fully experiencing Diagon Alley, once they've gotten inside¹.

We know that muggles are allowed in Diagon Alley, because we see Hermione there with her parents (emphasis mine):

"So you don't think I’m a match for Lucius Malfoy?" said Mr. Weasley indignantly, but he was distracted almost at once by the sight of Hermione's parents, who were standing nervously at the counter that ran all along the great marble hall [of Gringotts], waiting for Hermione to introduce them.

^{Chamber of Secrets Chapter 4: "At Flourish and Blotts"}

In fact, it's been suggested on this site before that muggles can, in certain situations, simply enter through the Leaky Cauldron.

Of course, I expect most muggles would have a bit of a hard time processing what they were seeing and, as ThruGog mentions in comments, uninvited muggles would almost certainly eventually be rounded up, obliviated, and sent on their merry way. But in the meantime, there's no reason to believe that muggles are prevented either from entering or seeing everything Diagon Alley has to offer.

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¹ Of course, I would heartily expect it to be difficult for a muggle with no magical ties (for example, being the parent of a witch or wizard) to get there in the first place. It would be a bit of a blow to the International Statute of Wizard Secrecy if the city of London, for example, accidentally built a Tube station underneath it.