Ms. Revathi
The concerns you've raised are pretty genuine.
These are purely my personal views and I take total responsibility to whatever I say here:
I really do not know what your experience is like, however, must tell you that you need sufficient standing, maturity, and above that you as a professional enjoy unquestionable respect both within and outside the organization, to effectively handle an exit-interview.
In fact, some people (who don't want to close the doors for future, who might look at a return back), will give you a balanced and honest feedback - positive and those that weren't (with constructive suggestions too). \
The converse is true too, that there will be some who are so excited about their new job, that they will be critical of everything that they experienced being with you.
There is another category too which will only gloss over the whole thing, sound good and sweet, and may be not tell you the truth too and cry every reason of emotion to convey their departure.
Anyway for your evaluation, you will need to have some sort of background information on such employees as to what their contributions were when they were with you, what was their attitude like etc., to probably arrive at some what good conclusions. And then there must be a process by which the information is shared with those who are at the decision making table to ensure concerns if any are addressed, in order to reduce, if not be able to arrest attrition.
You will be well advised to take a detailed read of this too :
exit interviews - tips for interviewers, employees, sample exit interviews questions and answers guide
Here are some more links for your information:
Sample Survey Employee Exit Interview Employee exit interview including evaluation of relationship with co-workers, The Job, Benefits and company evaluation.
http://aia.org <link fixed>
This might lead you to more questionnaires on Employee Engagement, Employee Satisfaction etc., :
Employee Satisfaction Survey Questions: 3 Sample Templates You Can Use Today | Qualtrics Blog