Does my H-1B or L-1 employer keep withholding FICA even after I plan to leave the U.S.?

Yes. As long as you're working on H-1B or L-1 as a resident alien or a nonresident who isn't an exempt individual, your employer must withhold Social Security and Medicare on your wages, regardless of whether you intend to stay. Plans to leave don't change withholding. The only relief is a totalization agreement with a certificate of coverage keeping you on your home system, and India has none, so Indian workers pay full FICA. Those contributions can still pay off if you eventually earn 40 credits for benefits. If you leave before then without a totalization agreement, the contributions generally aren't refundable. The Social Security Administration lists totalization agreements at ssa.gov.