There is no possibility for NEET being cancelled because it’s the only basis of admissions for medical colleges in India except AIIMS and JIPMER. Till a new examination is set there is least chance to replace NEET and as it is Supreme Courts order it might be hard for TN or any other state to opt out of it.

Coming to your drop, I would say it is a risk to drop 3rd time but as your age is mere 18 I believe you should try at least once. Join any coaching institute if you feel so, study smart and I am sure you will reach your goal.