OA shud be D .. E is not possible
Defination of Muse :https://dictionary.reference.com/search?q=muse
Deprived of his witty and loyal muse, Dillon McKay, which he defiantly relied on for direction and inspiration, lost the ability to compose the moving musical pieces that had made him famous the world over.
(A) Deprived of his witty and loyal muse, Dillon McKay,
which he defiantly relied on for direction and inspiration (which points to Dallen and distorts the meaning )
(B) Deprived of his witty and loyal muse, Dillon McKay, defiantly relying on for direction and inspiration (here though the construction sounds a bit awkward at first sight but is not incorrect (as per me) ; defiantly relying correctly modifies Dillion Mckay BUT it changes the original meaning of the sentence.)
(C) Dillon McKay, deprived of his witty and loyal muse,
who he had defiantly relied on for direction and inspiration (muse is NOT a person/group so who is wrong)
(D) Deprived of his witty and loyal muse,
which he had defiantly relied on for direction and inspiration, Dillon McKay (which correctly modifies the Noun just before it )
(E) Deprived of his witty and loyal muse,
who he had defiantly relied on for direction and inspiration, Dillon McKay (same as C )