1. Severus and Harry, each vowing to start life anew after past missteps, find themselves on the same banana boat cruising through the Panama Canal. Hilarity and/or angst ensues.
2. Post-war. Severus has "died" in the Shrieking Shack. Harry was disappeared. They "meet" in their Animagus forms (be creative) and the rest is history.
3. Harry has squirreled away the not-really-quite-dead Severus to Grimmauld Place where he helps him heal in secret while the wizarding world celebrates the end of Voldemort, recovers and rebuilds itself. Severus' convalescence is long and he gets to know a Harry he never suspected exists.