Ev, I took a close look at the video, and the 500V's appear to be non-modular.
I'm sure they probably had a large cache of them on hand for telethons, phone banks, etc, just as they had trailer mounted banks of payphones.
I'm sure they ran the numbers comparing cost and time for cleaning vs replacement of the switch, and probably considered other factors such as available space for the new switch(s), availability of new switches, etc.
Apparently, some equipment _was_ replaced with ESS.
According to
https://www.privateline.com/issues/p.l.No11A.html, which quotes from the book _Telephone: The first hundred years_ by John Brooks (out of print at the time the article was written, although it looks like there are ~200 copies available from Amazon
https://www.amazon.com/Telephone-First-Hundred-John-Brooks/dp/0060105402), there were 12 exchanges, and 5 toll switches in the building, serving 104,000 lines (170,000 telephones).
"The work to be done in the damaged building varied all the way from installing new ESS equipment and writing computer programs for it to cleaning smoke-damaged relays with toothbrushes and Q- tips. A couple of happy circumstances speeded the work along. One of these was the fact that the the third floor of the burned building happened to be standing vacant at the time, thus providing space for the rapid installation of an entirely new main frame for handling trunk calls, which was shipped by cargo jet on February 28 from Western Electric's Hawthorne works. Another was the convenient availability for emergency use of excess switching capacity, from the ESS installations at Seventh Avenue and Eighteenth Street and at New York Telephone headquarters at Sixth and Forty-second. Such capacity could temporarily accommodate 28,000 of the 104,000 served lines."
