Would miss if they were gone:
James Keelaughan
Tom Paxton
Slim Dusty
Bill Staines
Tom Chapin
John Williamson

Though not songwriters these folks keep finding good songs to pass on:
David Holt
Cathy Barton & Dave Para

Do miss
Phil Ochs
Stan Coster
Jimmie Rodgers
Dave Macon
Otis Pierce
Grandpa Jones