This is the 6462nd most frequent Korean word.
없으며
"없으며" means "and does not exist" or "and there is no."
Here, '없으며' expresses the location where he isn’t (school) and links it to the probable alternative location.
그는 학교에 없으며 집에 있을 겁니다.
He is not at school and will probably be at home.
'없으며' is used here to state the unavailability of the book and connects to the proposed action.
도서관에는 이 책이 없으며 다른 도서관에서 찾아야 합니다.
The library does not have this book, and you need to look for it in another library.
The word '없으며' indicates the absence of something (windows) and connects to the subsequent related observation.