first of all if you lose your follower you will have to find another or reload your last save.Fawkes the super mutant is located in downtown dc at the museum of history he requires god karma there is dogmeat in the scrapyard he requires no karma and with the level 22 perk " Puppies!" you will be able to get one of his puppies in front of vault 101 there is clover in paradise falls witch your have to have neutral karma and buy her from euolgy there is jericho in megaton you must pay him and have bad karma and one wandering mer chant will sell you a robot. fawkes and the brotherhood of steel person are extremely tought and never die.dogmeat dies alot but is a scavanger for ammo weps chems and food clover and jericho are worth their money but die easily
I've had Fawkes die on his own merit a few times. Wandering the Wasteland, sometimes Fawkes will have a hard time keeping up with me because he can't jump or climb down cliffs like I can, so he has to run around the long way to reach me again. A few times he never shows up and a message pops up on my screen saying "Note- Fawkes has died. Click OK". Restarting saved games brings him back temporarily for a while. But then one time I entered a building, he didn't, and I went back outside to see what was keeping him. At that very moment, Fawkes falls down dead for no apparant reason! Followed by the note that he has died again, click OK. So at least for me, Fawkes was not invinciple.I just decided to go on without him. Maybe I'll go buy Charon to take his place.