At some point, Zygor was destroyed. Accounts differed as to what the cause of this was and when it happened. According to one account, the planet was destroyed in the war against the Xaranti. (PROSE: The Bodysnatchers) Another account given by the Zygon Broton in the 20th century said his world was destroyed in a "recent catastrophe". (TV: Terror of the Zygons) Another account, given by Elizabeth I who had been posing as a Zygon in 1562, said that the Zygons lost their world when it burned in the first days of the Time War. (TV: The Day of the Doctor)
I also wanted to note that a lot of users, I found on the Web claimed Dugi’s Guide to be faster. However, all these users had either used Zygor Guides for very little time or had not used it at all. I have to give a point to each Dugi’s Guide and Zygor Guides as they both deliver a great lvling speed. For all you Dugi’s guide users out there who really feel that Dugi’s Guide is faster, I will give Dugi an extra point. If there really were a difference, it wouldn’t be by much.