Mid-century books that stand the test of time

I belong to a local group of booksellers called The Las Vegas Bookmans Guild. 
It’s a loosely-knit group of people who own used, out-of-print and collectible bookstores and willingly share their uncounted years of experience with fans (like me).

The group meets once a month at a predetermined restaurant to discuss various topics related to books.

Last week, before and after a food and drink (mostly iced tea, water and one glass of "grape juice") the topic of discussion focused on mid-century authors whose books survive – books that readers and collectors want to read, read again, or have available to read, books the booksellers receive requests for time and again.

Among the writers were James Thurber, Cornelia Otis Skinner, L. Frank Baum, Daphne du Maurier, and others on a list I compiled after the meeting, put in the pocket of my jeans then promptly washed! (Does the word airhead apply here?)

I’m wondering in this electronic publishing era, which authors (and their current titles) still be in demand in fifty years?

Any thoughts?

P.S. An interesting poll on goodreads lists titles chosen by readers as survivors.