The Excalibur survived an attack by the Borg during a night shift sometime prior to 2368. Several members of the crew, including Marika Wilkarah, were assimilated in the encounter. (VOY: "Survival Instinct")
In 2368, the Excalibur was undergoing a major refit and repair at Starbase 234. It was commandeered by Captain Jean-Luc Picard to serve in a Starfleet blockade of the Klingon-Romulan border during the Klingon Civil War. During that mission, it was commanded by Commander William T. Riker, with Lt. Commander Geordi La Forge as first officer since the Excalibur's crew had been reassigned due to the extent of the refit. (TNG: "Redemption II")
|USS Enterprise-C • USS Excalibur • USS Horatio • USS Yamaguchi • USS Zhukov|
The Excalibur was a reuse of the USS Enterprise-C studio model with the modifications introduced on the USS Zhukov.  New footage of the Excalibur was briefly seen as the fleet departed for the Klingon border, however, some stock footage from TNG: "Yesterday's Enterprise" was also reused.
As the Excalibur mentioned in "Survival Instinct" had to be in service prior to 2368 and Riker's ship from "Redemption II" probably wasn't a new ship, it can be surmised that they were both the same vessel and the Excalibur somehow escaped the Borg without being destroyed. It was not made clear whether or not the Excalibur's encounter took place during the 2366-67 invasion, but it could explain why the starship would need a refit long enough to warrant reassigning its crew.
The Excalibur became the star of Peter David's Star Trek: New Frontier novel series and was later destroyed and replaced with a new Template:ShipClass starship Excalibur. Captain Morgen, a former crewmate of Captain Picard's from his days on the USS Stargazer, was mentioned as having commanded the Excalibur for many years in Michael Jan Friedman's book Reunion. It was then commanded by Captain Morgan Korsmo just before the start of the New Frontier series. Korsmo was killed fighting the Borg, and was an old Academy classmate of Picard.