There are a few things robots will lack. Most importantly, those will lack the facial expressions of the umpires...like our very own Nadir Shah's.
Faislami apart, it's not about robots vs umpires. Robots can't even get close to what umpires can do...such as rational thinking, decisions based on situations, sense of power, using personal judgements, taking decisions, etc. Technologies that are brought out these days are only for making it easier for umpires in taking decisions. Nothing else IMO.