Are you still paying your "electric, gas or propane bills. Include water and sewer, for some areas if customers didn’t have their own wells or septic tanks." If not, is mdmathis6 counting you among the dead?
There were people in Erwin that thought my wife and I were dead until we turned up at a town shelter several days later. (We had left town to stay with a friend.)
No...but it makes the numbers easier to parse and to track...plus in combinations of other methods the scale of the numbers of the missing and dead can be ascertained and adjusted...hopefully downward as people are confirmed as alive vs missing or dead!
You are focused on one part of the methods I have suggested...the lack of activity of either hundreds or thousands of bank accounts based in that region is probably the best EARLY indicator of the scale who might be still alive, dead or missing.
The IRS is fanatic about making sure white Republicans are paying their fair shares and are not defrauding them. Missing moneys from with-holding accounts will be tracked as will non filing of tax forms next spring. They will be able to track and measure large scale anomalous numbers of missing forms and moneys coming from that area fairly quickly!
If Mr and Mrs X had been filing forms and suddenly they are not and their bank account has been sitting idle, it will be noted eventually.