> Whereas different dialects of Mandarin may not be mutually intelligible

Except for some slang words which nobody would use in business anyway, Sichuanese is largely intelligible to native Mandarin Chinese speakers if spoken slowly and repeated a couple times. People from Sichuan can also speak standard Mandarin. The written language is identical.

As for Taiwan and China it is even less an issue. The very few words that are different may be the source for some humor sometimes but that's it. It's kind of like how British people say "lift" and Americans say "elevator". If you're not brain-dead you'll figure it out pretty quickly. When you see a sign that says "lift" you don't panic and say that it's not intelligible, you can make some sense of the word.

Indeed, Hong Kong Chinese word for elevator is literally "ascend-descend-machine" in Chinese whereas in China and Taiwan it is "electric-ladder". It's not hard for one speaker to understand what the other is trying to say.

It's a non-issue in practical terms.