Do you have some kind of mods installed (restoration project for example)? to me it seems like something has overwritten/deleted feargus from where he should be, or atleast he seems to be invisible for some reason.
anyway to the problem itself, try downloading
savegame editor and editing the variable for the mission, while this might not bring feargus back it might get you through the door so you can continue with the quest/game.
open the save what you want to edit and in GVARS tab find 168:GVAR_NCR_TANDI_WORK=0 (or atleast it should be 0) and change it to 1, you also notice that number 169 is the variable for tandi accepting the job which is the reason i think this should open the door for you. (the number might be off in case you have mods or other tweaks installed, i just installed the game to see if there was a variable for the quest so my game is vanilla and some differences might occur.)
needless to say take a backup of your saves before editing anything so it won't atleast make things even harder should something else get corrupted when editing the save, hope this helps.