To, Google Now A Days All pages are dropped from site day by day.. If you going for big update then please give some instruction in you blog and tell where the end of this updates. Because day by day site pages are deindex.. I am only not Facing This Problem but many webmaster facing this problem. Or tell us which type of updates you are working on...just give us some guideline..what can we do in this situation.. I hope google team see this and give proper answer. From, Dhaval