This clearly depends on how severe the damage is. If there's a slight crack in the glass, people would still call it a window. If glass and frame are lying about, smashed into a few thousand pieces, no one (except an eccentric philosopher) would say that what's left is a window.

So how severe -- you will ask -- may the damage be exactly? This depends on standard use of the words of our language. Interestingly, things may cease under one description and continue under another. After some creative modification, what was a Hercules statue is still a statue, but not one of Hercules. After further modification it's no longer a statue at all, but still a piece of bronze. Similarly, when a caterpillar turns into a butterfly, a caterpillar ceases to exist, a butterfly begins to exist, yet an animal continues to exist throughout.

Philosophers have argued a great deal over whether what we say about such transformations is merely conventional (having to do with the words we have in our language and how we use them) or whether what we say can track (or fail to track) some truths about how matters really are (as your question seems to suggest).

Philosophers have analogously argued about the deeper issue that we tend to think of every such transformation as involving some underlying thing or substance that persists: When water turns into ice, H₂O persists. When H₂O disintegrates, its chemical elements (hydrogen and oxygen) persist. When these elements get transformed through a nuclear reaction, elementary particles (electrons and protons) persists. Etc. Is this just the way we think, or is this the way things turn out to be -- or perhaps the way things turn out not to be once our physics is sufficiently advanced? (Think of Einstein's formula about how matter and energy can be transformed into each other: E = mc².)