Question: This is all horribly nebulous, and I understand it.

But are there any examples in history, when any existing empire had dissolved and was afterwards recreated to more or less the same territory it occupied during its peak for any meaningful period of time (let's say 50+ years)?

I welcome suggestions about how to make this question more precise, but obviously I am looking into current aspirations of some people in Russia, who speak of "uniting Russia" to its historical 17th century borders.

Answer: 
The Eastern Roman Empire (Byzantine Empire) fractured into several states after the Fourth Crusade.

[![enter image description here](https://i.stack.imgur.com/1UWkV.jpg)](https://i.stack.imgur.com/1UWkV.jpg)
Map of the aftermath of the Fourth Crusade from [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:LatinEmpire2.png), around 1204.

Later, in 1261, the Empire of Nicaea succeeded in recapturing Constantinople from the Latins, and both claimed, and was generally recognised as a return of the Eastern Roman Empire.

[![enter image description here](https://i.stack.imgur.com/dOvwo.png)](https://i.stack.imgur.com/dOvwo.png)
A map of the Eastern Roman Empire around 1263 also from [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:1263_Mediterranean_Sea.svg). The green line shows the expansion of the Ottomans by the 1326.

The territory is certainly vastly less than the Eastern Roman Empire occupied at its peak, but is pretty close to the territory held prior to the fourth crusade, so may still be of interest.
The [Second Turkic Empire](https://en.m.wikipedia.org/wiki/Second_Turkic_Khaganate) was founded in 682 CE, about 50 years after the end of the [First (Eastern) Turkic Empire](https://en.m.wikipedia.org/wiki/First_Turkic_Khaganate).

The [German Reich](https://en.wikipedia.org/wiki/German_Reich)
was founded in 1871, about 65 years after the end of the [Holy Roman Empire](https://en.m.wikipedia.org/wiki/Holy_Roman_Empire).

Plus there are of lots of current nation states that trace their roots to some previous kingdoms (or similar) and that at some point were incorporated into other states. E.g. Poland, Portugal, Korea, Egypt, Israel etc etc.