On stardate 56344.5, in a timeline altered by the Borg, the Maverick was investigating subspace distortions at a turbulent nebula. After it had engaged its warp drive, the Maverick's warp field was disrupted by one of the subspace distortions resulting in the loss of its starboard nacelle. The ship spun out of warp, a series of explosions ripping it apart.
At a later briefing conducted by Admiral Kathryn Janeway, the subspace distortions that caused the Maverick's destruction, as well as that of the USS Courageous, were declared to have been caused by the Borg of the future attempting to assimilate the past utilising a time travelling tachyon wave. (ST - Alien Spotlight comic: "Borg")