If Wales, Gardner, and Moeller all had a bad batch of crispy Mandarin beef and perished, who would take over?

We’re talking about Jimmy Wales, Sue Gardner, and Erik Moeller, all of the Wikimedia Foundation, of course. And don’t belittle the chances of this hypothetical happening — it already came terrifyingly close, once already: https://www.flickr.com/photos/frieda/1729725629/ Now that Mike Godwin is gone, and the Chairman of the Board of Trustees is …

Is the dialect of Mandarin Chinese that is spoken in Beijing the same as or similar to the one spoken in Xian?

I am traveling to both cities and am hoping that if I buy and study a Mandarin phrase book, that will help me to be able to communicate in both cities. However, I recognize that Mandarin Chinese has many dialects. Does anybody have any practical advice here?