Mr.Fogg and Passepartout came to India and they bought an Elephant. It was about 2000 pounds. After they were traveling they saw some Indians planning to do a suttee. Suttee is sacrificing people alive. Mr.Fogg and Passepartout planned to save the woman who was about to get suttee. That night they went into the temple and tried to save the woman but failed. The next day after they failed their mission they had a second attempt. The Indians burned the woman but then! The man who was next to her was alive! People were  surprised! It was Passepartout who saved the woman.

Correction:  Student's sentence   Corrected sentence        Grammar explanation       Better 

Mr.Fogg and Passepartout came to India and they bought an Elephant.

This sentence is correct.

It was about 2000 pounds.

This sentence is correct.

After they were traveling they saw some Indians planning to do a suttee.

This sentence is correct.

Suttee is sacrificing people alive.

This sentence is correct.

 Mr. Fogg and Passepartout planned to save the woman who was about to get suttee.

This sentence is correct.

That night they went into the temple and tried to save the woman but failed. 

This sentence is correct.

The next day after they failed their mission they had a second attempt.

This sentence is correct.

 The Indians burned the woman but then!

The Indians burned the woman, and then something unexpected happened.

The word "then" is an adverb that indicates a sequence of events. It suggests that the action of burning the woman was followed by something else, but the original sentence doesn't specify what that "something else" is. The revised sentence maintains the same structure but clarifies that there was an unexpected event following the burning of the woman.

The man who was next to her was alive! 

This sentence is correct.

People were  surprised!

This sentence is correct.

It was Passepartout who saved the woman.

This sentence is correct.