I have an area of dead brain cells caused by severe dehydration.i ask if someone knows if this area gets bigger by time?

Best is to consult a neurology physician, who can determine if the area described is only due to "severe dehydration", and not connected to another disease entity.

Not feasible to assess the significance of your so-called "dead brain cells" without visualizing the radiological images and reviewing your medical history. In absence of further deleterious circumstances, there would be no reason to expect an area of encephalomalacia to enlarge. A virtual consult might be of further value (www.connect@healthtap.com)