The Last Stand of The X-Men was the final conflict in original timeline. The X-Men had their final battle against the Sentinels as they try to protect Kitty Pryde has she holds Wolverine in the past.
After the Battle of Moscow, where Kitty successfully sent Bishop's consciousness back to warn the Free Mutants of an upcoming Sentinel attack, they toke refuge in a temple in China. They are then located by Professor X, who arrives at the temple with Storm, Wolverine, and Magneto.
As the Sentinels break into the vault to kill the final four mutants, they and the mutants vanish from existence. With the mission to stop Mystique successful, history was changed mostly for the better. A new timeline of events took place changing everything after 1973, meaning that none of the events of these wars ever happened. Wolverine returned to 2023 to discover that it was a peaceful world, no longer war-torn. The X-Mansion was fully functioning and full of mutant students and Cyclops, Jean Grey, Beast, Rogue, Iceman, Colossus, Storm, Shadowcat and Professor X were all alive and well.