God, all of you here are educated professionals and yet you're arguing about basics. Everyone who's ever worked and has some knowledge of business , knows EACH AND EVERY CONTRACT IS DIFFERENT FOR DIFFERENT COMPANIES AND DIFFERENT PEOPLE.
A contract is between the company and the employee and can even differ from employee to employee. As far as Ema cast is concerned, everyone's contract is different from each other. Its based on what they bring to the company. Some contracts are air tight and others are lenient. So we don't know what contract Rachana signed so we cannot comment on it,
Also Ashish, Rachana , Shilpa and several other actors from other serials have often complained saying they only come to know about their scenes being told to them on the sets, being made to wait while they actually right the scene on the set. So NO RACHANA DID NOT KNOW ABOUT HER REPLACEMENT. Also, Rachana would not know coz the pH was still negotiating with Asha. Asha is definitely not shooting till date as she would have tweeted about it to her fans about how wonderful it is to have started shooting etc..
Other reason is spoiler pics and news...they only come out a couple of days before the actual scene not coz they want people to get them fresh,but coz they're shot at that time. In fact if they were shot before they would be released in order to build the moment but they cannot do so til they 're actually shot. that is another proof that actors do not know about their scenes till day before.
So please verify your facts before accusing someone of acting sweet...Rachana has always been the most professional actor ever...and we respect her a lot.