sonic and shadow live in the green hills area for a decent ammount of time after their marriage, then they leave and travel the world together, running through fields and woods, beach horizons and mountain peaks. no one knows where they are ever, they keep in touch obviously, but rarely do any of their friends see them after they leave
everyone knows about sonic and shadows wereabouts, if you dont youre missing out!
after literal decades of traveling over all types of land, sonic(whos old as shit by now) and shadow(looks old asf, he'll regen soon dw) finally go back to their true home in green hills, seeing all their friends again after decades of just short visits and constant calls.
and then after their friends start to slowly creep to their last years sonic and shadow start looking for a more secluded area to live, obviously they spend all their friends last moments with them. but once they all pass, sonic and shadow leave to live on a little mountain side in a cute little cabin, its eclectake and crazy looking, but its home<3
shadow continues to grow old looking, and then regenerate(basically just shed the old lookin crap) while sonic becomes more grey and old. though he lives far longer than any of his other friends, hes not immortal. he passes while with shadow sitting on a bench under their apple tree. his head on shadows shoulder looking over their gorgeous view of the mountain range theyve called home for over 40 years.
shadow doesnt realize at first, but once he does he just cries, hes glad he was with sonic in his last moments, but the heart will always break no matter how calm the last moments might be. sonic is burried under the apple tree.
shadow gets inspired after his husbands passing to become a kinder soul, though he never leaves his mountain range so he becomes a secluded man, he farms his own crops and makes his own meals, only going out of town to get chilli ans hot dogs for his weekly chilli dog while he sits alone at his small circle dining table, looking at his photo of his dear husband, from basically a millenia ago.