>>What about the typical office workers who crunch spreadsheets, process HR details, handle Accounts Payable, Accounts Receivable, etc? Are they going to function without a desktop?

Those A/R and A/P tasks are slowly morphing or even disappearing.
In this case, business is far behind individuals who have moved more quickly, but
more and more of our clients are ordering inventory and sending, receiving and paying bills electronically.
Here's something you can say with certainty:

Someone who plans to make a living selling paper checks is in for trouble.

I personally write less than 5 a year and our clients are gradually moving off them.
Payroll in most companies has become largely paperless with payments and documentation going to employees and government agencies electronically and alll the typical end of quarter and end of years tasks which once took days and weeks, now happen in hours with a fraction of the previous operator and machine effort.
The once tedious bank reconciliation is largely automatic.

So, yes it's conceivable that the desktop, as it relates to some of those functions, will be obsolete because of the way those tasks are changing.