There was no suit.
The libretto was published in 1935 with full credit to Dubose Heyward as librettist and lyricist.
Title- "Porgy and Bess, An Opera in Three Acts, Libretto by Dubose Heyward, Lyrics by DuBose Heyward and Ira Gershwin." 1935, Random House
The first edition was limited to 250 copies, all signed by George and Ira Gershwin, Dubose Heyward, and the director of the opera, Rouben Mamoulian. It was a beautiful book with piano and vocal scores, bound in red morocco, in a slipcase.
Copies are on offer, from $15,000 to $40,000; it is the most desired of all American music books.

Dubose Heyward wrote no other librettos and composed no other music for public consumption, thus never received the acclaim accorded the Gershwins.
His book "Porgy" was briefly popular, but the subject matter, poor Blacks, was not one that would reach out to a broad readership.