Can autocad be replaced by revit in future?

I do not think so. Both might be equally important in it's own right-but I don't see AutoCAD being overridden anytime soon. It has many powerful tools for2D drafting, which I believe no other software can supersede at present.

In my opinion            , 

Yes.

Not Completely, but at least70%-80% of work, will be carried out with the help on Revit !! As AutoCAD is a very user friendly and powerful tool however need to go through unremitting updating.

CAD is an important software in field of engineering, Although Revit help in understanding the project virtually, it helps in coordination of all the MEP services. But is not possible in revit to make Stage-C to Stage-E drawings. 

The stages mentioned above are concept to detail designed. The further stages are very well coordinated in Revit.

Thus as my experience both software serve different purposes.

I believe No, Both will be there cause each of go its own track.

the AutoCAD is mainly for drafting wise .. on the other hand Revit is a BIM tool that simulate the reality

both in architecture field got it's own positives and negatives .. yet both are important.

Business wise, As AutoDesk, why shall i stop selling a successful software for another .. i shall sell both 

Maybe, but of course Autocad is the most common software use all over the world now.

may be that happen but i think Autocad will keep the original AutoCad .

maybe, if AutoCAD change some features

Sure , Although the Autocad is the most common software but it depends on "   how much powerful gained by the program "

so revit as it  is easy and flexible software ... i think it should be the one to replace Autocad