Yeah mother knew fateh since childhood. That doesn't disprove the possibility of the real Fateh missing and Ranveer posing as him. In fact he doesn't even need to be a look alike coz Fateh was raised in London and nobody knows how he looked when he grew up.
Also if you notice , in that scene when Mother says she knew him from childhood, they don't show Fateh reciprocate or acknowledge anything. So all the more possible that it is not the realFateh
agree with @sukhminder,not only mother but vicky too fateh's friend since his childhood,i mean thhey are shown togather in childhood...in last night episode vicky said to fateh that you use to copy me in exams...so not only mother but vicky too acnowledge fateh from their childhood...dont want to pull this further just want to say that ranveer & fateh are different person ranveer already died...as for as artcles are concerned every article regarding this including so many daily newspapers print ashish's photograph & said that ashish will be back as new avtaar in the show after ranveer's death.