Option 1: Himanta Biswa Sharma - This option is not the correct answer. Himanta Biswa Sharma is a politician from the state of Assam in India and has not been appointed as the head of the seven-member committee to look into revenue shortfall after the GST roll-out.

Option 2: Thomas Isaac - This option is not the correct answer. Thomas Isaac is a politician from the state of Kerala in India and has not been appointed as the head of the committee to look into revenue shortfall after the GST roll-out.

Option 3: Sushil Modi - This is the correct answer. Sushil Modi, a politician from the state of Bihar in India, has been appointed as the head of the seven-member committee to look into revenue shortfall being faced by the states after the GST roll-out. The committee will also suggest steps for augmenting collections.

Option 4: Capt Abhimanyu - This option is not the correct answer. Capt Abhimanyu is a politician from the state of Haryana in India and has not been appointed as the head of the committee to look into revenue shortfall after the GST roll-out.

In conclusion, the correct answer is option 3: Sushil Modi.