If I weren't here, this office would be chaos in three days.
Literal
I [subject-が] not-existed-[conditional-たら], this office [topic-は] 3-days [in-で] chaos [copula-ですよ].
カオス is a loanword from 'chaos,' used casually in modern Japanese. ３日で 'in three days' — で marks the time frame. The speaker is humorously (or seriously) asserting their indispensability. A self-aggrandizing but relatable workplace boast.