From wiki: https://en.wikipedia.org/wiki/Sidley_Austin
They conveniently only lost one out of 600 employees on 9/11.
The terrorist attacks of September 11, 2001 personally affected the employees of Sidley Austin. Prior to the merger creating Sidley Austin Brown & Wood, which took place just four months before the September 11, 2001 terror attacks, the head office of Brown & Wood was in the World Trade Center, while Sidley & Austin New York office was located in offices on Third Avenue. Out of 600 employees who worked in the World Trade Center at the time of the attacks, one perished, a switchboard operator, Rosemary Smith.[24][25]
Sidley Austin reopened its New York office on Monday, September 17, 2001 in the old Sidley & Austin office on Third Avenue which it had planned on closing on September 16. Instead, it leased four additional floors in that location, in a deal completed less than three hours after the collapse of the World Trade Center. Sidley Austin later opened its permanent new office in the Equitable Center building on Seventh Avenue in July 2002.[24]