At times, movies which are launched with a set of stars leading the cast undergo major changes, with the leads getting replaced and in most cases, these movies have become superhits as well. Here's an interesting compilation of few biggies which had the heroes/ heroines opting out after shooting, due to various issues/ differences.

Endhiran:

The 2010 sci-fi entertainer Endhiran, which marked Superstar Rajnikanth's second collaboration with director Shankar after Sivaji, was supposed to have Ulaga Nayagan Kamal Haasan in the lead and Preity Zinta playing the female lead. While stills from the photoshoot of the movie, initially titled Robot during the late 90s, created humongous expectations, Kamal Haasan could not work on the project, and it took close to a decade for Shankar to realise his dream with Rajnikanth and Aishwarya Rai, and the result was a blockbuster.

Ghajini:

The story of the short term memory loss patient, industrialist Sanjay Ramasamy, Ghajini directed by AR Murugadoss was released in 2005 with Suriya and Asin in lead roles, and turned out to be a blockbuster. However, not many know that this movie was initially support to happen with Ajith, who played the lead in Murugadoss' debut Dheena, but after initial photoshoots, Ajith opted out of the project due to differences with the producer. The movie was rechristened Ghajini, and was a superhit, not just in Tamil, but also in Telugu and Hindi.

Aadukalam:

Vetrimaaran's second direction venture which released on Pongal 2011 and turned out to be a critically acclaimed and commercially successful movie which won Dhanush, Vetrimaaran national awards. Aadukalam marked the debut of the now popular star of Bollywood, Taapsee Pannu as the Anglo Indian girl Irene, but initially it was Trisha, who was supposed to play the role. After initial shoot, Trisha opted out of Aadukalam, and after 5 years, paired with Dhanush in Kodi, also produced by Vetrimaaran.

Ko:

Director KV Anand, after the mega success of his Ayan with Suriya, opted for another racy entertainer with the protagonist playing a cameraman working with a newspaper, and had Jiiva and Karthika playing the lead pair. Karthika made her debut with Ko, and the movie which was dubbed in Telugu as Rangam became a blockbuster there as well, and remains the biggest blockbuster in Jiiva's career. However it was actor Simbu, who was KV Anand's initial choice to play the lead, and after initial photoshoots, the actor opted out of the movie.

Friends:

The 2001 blockbuster starring Vijay and Suriya in lead roles was the Tamil debut of director Siddique, and was the remake of his very own Malayalam blockbuster. While initially, Friends was launched with Jyothika as Vijay's pair and Suvalakshmi as Suriya's pair, the cast underwent a change, with Jyothika getting replaced by Devayani and Suvalakshmi replaced by Vijayalakshmi. The movie became a blockbuster, which ran for more than 200 days.

Unnai Ninaithu:

The 2002 flick Unnai Ninaithu had Suriya and his Nandha pair Laila and Sneha sharing screen space, and the typical Vikraman brand family entertainer with a simple plot and an appealing screenplay became a success story. But little do people know,it was actor Vijay who was to play the lead in the movie. Vijay, who had worked with Vikraman in the 1997 blockbuster Poove Unakkaga, which was the first biggest blockbuster in his career, started shooting for Unnai Ninaithu with Laila, but after few days opted out of the movie, as he felt it too similar to Poove Unakkaga.

Nerukku Ner:

The 1997 movie Nerukku Ner had many highlights associated with it - the Vasanth directorial was produced by director Maniratnam, it marked the return of actress Shanthi Krishna, and was also the debut movie of actor Suriya. Nerukku Ner was initially launched with rivals and rising stars Vijay and Ajith as the leads, and was supposed to be their second movie together after Rajavin Parvayile. However, after few days of shoot, Ajith quit the project, leading to Suriya's entry in films. Nerukku Ner was commercial successful as well.

Naan Kadavul:

Released in 2009, this intense drama from director Bala had Arya and Pooja playing the leads, and was a critically acclaimed movie which won Bala a National award for direction. The movie presented a whole new version of Arya and Pooja who were known previously for their fun roles in commercial entertainers. Initially, Naan Kadavul had a grand launch with Ajith and Bhavana playing the leads, and Ajith underwent a major physical transformation losing oodles of weight and growing hair, but unfortunately, had to opt out of the project.

These are just few samples of "Your loss is my gain" case of one star quitting a project and another star entering it and scoring a success. There are many more such cases of top stars quitting mega projects, which have happened in the past, and will continue happening in the future as well!