Japanese media doesn't end shit well anyways.
Here, I'll write a probable end for those series, plot outline only.
Full Metal Panic- Sagara's military career takes him away from the school. He writes to Chidori every day and promises to marry her as soon as he gets a debilitating injury.
Haruhi- Kyon goes to college and becomes an accountant. he looks back on his days with Haruhi nostalgically, and meets her one day on his way home from work on a train.
Zero no GAY-Saito gets laid. However, the sexual climax with Louise causes her to voidwarp them into modern day japan. Commence OMG NOT AN END BUT FUN TIMES WILL BE HAD end.
Spice and Wolf- Horo eats an apple.