The second half of Hum Dil De Chuke Sanam is loosely inspired by the 1983 Naseeruddin- Padmini- Anil Kapoor film "Woh 7 Din" which itself was a remake of a South Indian Film.
The first half's plot is from Maitrayi Devi's Bengali novel "Na Hanyate" (English translation: It does not die) which was written in response to world-renowned scholar Mircea Eliade's semi-autobiographical novel "Bengal Nights". There are several resemblances, including the 'mirchi-eating' incident, which suggest that they are more than uncanny resemblances.
There are numerous films in several languages which have been based on literary works. There is nothing inherently wrong in that, except that in this case, Bhansali has not acknowledged the 'right' source of his work. We have heard that HDDCS has been based on a script told to him by one of his Gujarati fans. Really, Mr Bhansali? Or is it a case of acting naive and passing the responsibility of plagiarism to your Gujarati fan when one finds out?