Nukes can't effectively be detonated by India on its own territory in the case of a "deep incursion." They have a densely populated geography. India would effectively be committing suicide on every level with that option, politically, militarily, economically etc. Losing the war is a safer option for them compared to nuking its own territory, especially considering the resulting holocaust that would follow from a retaliatory nuclear strike.
If any full-scale conflict occurs in South Asia, it is expected to be very short, intense and conventional. Therefore, what matters here is conventional deterrence. And India is far behind in this front. Just as a case-study, look at the IAF's Rafale purchase, which is an indicator of what matters most: Air Power. Let's see what it adds to the equation. 2 Sqadrons of Rafales, 1 deployed in each theater (Ambala AFB in the West and Hasimara in the East). No. 5 Squadron at Ambala, oriented towards Pakistan, will be facing 50 Block IIIs (AESA + PL-15s) + *36 J-10CEs (AESA + PL-15s), while their second squadron is facing a legion of PLAAF AESA+PL-15s/PL-21s. The propaganda of the Meteor's supposed superiority is also just hype. Chinese AAMs have Dual-Pulse motors, which are arguable a better kinematic solution than the Meteor's ducted-air-compressor, which has a lot of variables effecting performance compared to a second rocket-motor. Also, the PL-15/21s AESA seeker is much more dangerous than the Meteor's seeker. We can run another analysis on the other magic silver-bullet that the Indians are hyping about (the S-400) but let's leave that aside.
TLDR: There is no conventional parity here, hence, no conventional deterrence. And that's going to matter more than nuclear deterrence.