In a realm, my freind and i had a nether portal and we died in the nether, we went back, the portal wasnt there, we returned to the spot a little later,it was there, we went back, it was there, i went in, got my stuff, want out, and i was in a totally different place, about 100 blocks away from our original spawnpoint, and we had never built a nether poral there before.