1)go to file manager.
2)go to the memory where is your game saved.
3)open folder "android"
4)find and open "com.gamesas.falloutshelter"
5)open "files"
Numericaly there is three vaults allowed.If your lost vault was on the first slot, then there must be vault1.sav and vault1.sav.bkp
6)copy vault1.sav.bkp to another folder
7)delete .bkp index
8)you got vault1.sav. copy it back to the game folder where you took it
9)it will say that you already have it, REPLACE IT
10)YOUR VAULT IS ON YOUR SERVISE NOW AGAIN!
ENJOY