..from guys you may not expect.
Many know Mendelssohn's efforts in resurrecting J.S. Bach's choral music in the mid 19th century. Of course, in terms of composers and musicians, Bach's legacy never disappeared. Guys before Mendelssohn, like Mozart and Beethoven were well aware of Bach's music, admired it and where influenced by it.
Then there's Liszt, many of whose works give a fair hint of Bach's influence. Not only his Prelude and Fugue on the name B-A-C-H (for organ, but there's also a piano version) but also that fugue at the end of the Sonata in B minor.
Brahms was also influenced by Bach and the other wigs. In Harold C. Schonberg's book, The Lives of the Great Composers, he conveys how Brahms said (or wrote) that if he'd composed the Chaconne from the Partita for solo violin #2, he probably would have killed himself at the sheer intensity & humanity of it, etc. In terms of Brahms' works testifying to this in some way, look to his variations on themes by Handel and Haydn respectively & more generally, the Baroque complexity of things like his Piano Quintet and String Sextet #2.
Another one is Saint-Saens, who was the first to play all of Mozart's piano concertos since the death of the composer. The counterpoint in the opening cadenza of his PIano Concerto #2 sounds decidedly Baroque, but also deeply expressive, which is what we associate with music of Romantic era. Listen to the Petite Symphonie for wind instruments by another Frenchman, Gounod, and don't tell me it doesn't sound as if he was well aware of things like Mozart's Gran Partita, also for wind instruments?
Bruckner did not care much for Beethoven (eg. he only consulted the scores of Beethoven's late quartets when composing his String Quintet in C). However, as one of the best organists of his day, I would bet he played a fair deal of J.S. Bach, Handel and other greats of the past. I think Bruckner was not much different than Brahms in building upon the past, of which he had a strong knowledge of (eg. his sacred works go back before the wigs to Palestrina, Schutz and Gabrieli).
Then there's Tchaikovsky who adored Mozart - eg. his Rococo Variations for cello and orchestra and also his Orchestral Suite "Mozartiana," are but two examples of this.
In Norway, Grieg with his Holberg Suite similarly reached back to old times, fusing that with the folk music of his own country.
& there are many other examples like these.
My point is that "back to Bach" (and the other wigs) was not only due to Mendelssohn, though he was of course pivotal in this movement. I'm saying there were others at the time doing similar things, esp. based on hearing their music.
Then of course we had this really take off in early 20th century, with musicians like Widor, Casals, Schweitzer, Ysaye, Landowska & so on, promoting Bach's and the other's music in their respective fields...