What do you think would happen if all the depositors went to ask for their money at the same time in bank ?

The bank would be at problem , as bank keeps only 15% of the total deposits(rest in under RBI). They won't be able to provide demand deposits to the depositors. 

Moreover , they would'nt be able to give urgent loans to people, so the people would have to get loan from informal sector. Which would decrease economic development of country.

the question u have asked is not possible "PRACTICALLY".

Yes, in case it happens, banks will be in short of funds

and as a last resort it will have to depend on the RBI for  ettling the problem.