There are a couple other things to consider about the change of names over time, such as how some voiced and unvoiced sounds can easily change between each other. For example, the letters 'P' and 'B' or the letters 'T' and 'D' can frequently, so, for example, in a few thousand years, London may be Lonton, or Pittsburgh may become Biddspurgh.

There is also the chance that some sounds may become transposed with each other over such a long period of time, so Pittsburgh in that could become something like Pisttbrugh.

Vowels could change significantly, even multiple times in such a long period of time, so Sydney may change to Sednay in just a couple hundred years, and then a couple hundred years later be Sudnah.

Also, while yes, as Kirkspencer mentioned, words tend to slur together and get shorter over time, it's worth saying that sometimes sounds will get added randomly, especially if they combine easily with other letters. The most notable letter (and the only one I can think of any examples for at the moment) is 'S' which can also be randomly taken out of words, both of which usually happen on the beginnings and ends of words. So with that in mind, Pittsburgh could become Spittburgh, or Scotland becomes Cotland.

And that's all just how any language can change over time just from the interaction of the native speakers with themselves. Once you get multiple cultures or multiple languages it could change even more, as pointed out by Creativetides and Tenia respecteively.