You left your dog, your most faithful companion, alone and untended in the harsh and unforgiving wasteland, with nothing but a "stay here, boy, i'll be right back" and a pat on the head, and you "forgot" about him? And now you just want to snap your fingers and magically have him back? You left the poor ol' fella exposed to the elements, awaiting on the burning sands for the return of his master in vain, yet AGAIN, and went on to gleefully punch a few holes in some unnamed critters, and now you don't even think that he deserves a mere couple hours of your precious time? Well, allow me to give you a reality check, mah boy. Your dog is critter food by now. His carcass is calcinating at some radscorpion nest in some god-forsaken hole, and it's all YOUR fault. It's a cruel world; It's a dog's world. He waited. You forgot him. You weren't there. You. Have. Failed. Him.
NEVER think that a bite of lizard barbecue and some half-assed Mad Max cosplay buys you the right to take love for granted. I think we have all learned an important lesson today. May we all meditate upon the feebleness of human loyalties and friendship, and on the vain nature of the heart of man. May this be an example for us all.
Seriously now, pal, happened to me once, i simply rolled back my save, the same way as when someone dies on you. This isn't gamebryo, so you can't just type a command to summon a npc from the void - i know it sucks, but sadly, it's the only way. :/