I wonder how much Chinese HQ19 Exo-atmospheric and HQ29 mid-course interceptors affect India's current deterrence posture.
As of now, I'm afraid there isn't really much of a
credible deterrence posture against China to begin with. Let alone taking the ABMs into account.
The reason for that is that I feel true credibility only comes with a survivable second-strike capability. While it appears the K-4 SLBM might finally be operational on at least 2 SSBNs, the problem with its ~3500 km range is that the submarines have to confine themselves to a relatively small portion of the northern Bay of Bengal in order to hold Beijing within reach. This can present a lot of problems if one has to deal with the possibility of Chinese SSN presence in the Bay.
A way around this could be to load up a sub and send it off on a months-long deterrence patrol somewhere in the Philippine Sea or the Pacific. But I doubt IN would be willing to do that especially when we don't have any SSNs to accompany/support/delouse it. SSKs are no good for this job.
And then there's the issue that the current SSBNs can only carry 4-8 missiles, each with a lone unitary warhead. Overall, the situation is far from ideal.
The only way to fix this is through the S-5 class SSBNs and their K-5/K-6 MIRVed SLBMs with intercontinental ranges. It's only then that an ability to hold Beijing under threat from pretty much any part of the Bay of Bengal (or even the Arabian Sea) will be attained. Each one of those boats will be able to carry at least 48 warheads (assuming 4-MIRV config) as opposed to just 4-8 warheads on each Arihant-class. The sea-capable nuclear arsenal will see a seven-fold increase once all four S-5s are commissioned.
Plus, arrival of SSNs under Project-77 will enable much more expansive deployment patterns. But that will all start happening only in the next decade.
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As of the ABMs, it's anyone's guess how good the Chinese ones are. I doubt they'll do much to change what needs to be done to punch through (more warheads, better penetration aids, maybe more novel RVs like some of the HGVs we're testing). The Chinese aren't deploying anything the US hasn't already done, and if the deterrence equation didn't change drastically there, I don't think it'd change much here either.
