Alka Yagnik is performing in North America, which has been planned months in advance. There was no way, Alka could have been in the show in India and then peformed here. So instead of gracefully saying Goodbye, the Channel and Production team decided to add Masala to her exit which was pre planned.
This is ok as long as it improves the TRP rating of the show. However when the show starts playing with the emotions of the budding singers, it is unethical.
Here is the link for Scheduled performance by Alka and Kumar Shanu.