I'm not a lawyer, so FWIW...
I believe a Motion to Dismiss is not considered "responsive" to the original complaint, although, in support of it motion, TCA lays out its whole case as to why IHSI's claim s/b dismissed.
I believe IHSI nevertheless has a right to respond to the MTD (within 14 days?), but not sure.
More substantive, I believe, is TCA's assertion in the MTD that it intends to file counter-claims and third-party claims against IHSI.
But it could all be gamesmanship... who knows.
And again, I'm not a lawyer, so take it FWIW.