>quickly scaled up
Quickly is more likely decades to reach appropriate as in case of rare earth processing. There's 20 years of supply chains entrenched in PRC that's not going to be replicated without substantial effort or time. That means allocating resources so strategic companies can survive while everyone else that relies on those inputs die. Btw, most of those experts needed to scale up elsewhere? They're from PRC in PRC building out PRC capacity for last 20 years. There's not enough experts globally to do such a task "quickly".
>Mutually Assured Destruction working between India and China
Yes, which is why the idea India would blockade PRC is fantasy. They fight with fists over barren rocks to prevent escalation spiral, and India has been firm in preventing QUAD into becoming a security alliance. They're not going to escalate to full scale war with PRC while eastern theatre command can shower most of India with missiles from barren Tibet while India has very limited ordnance to reach PRC strategic east coast or XJ. At least not for decades.
There will conceivably be a time when PRC is disentangled from global supplies chains or PRC neighbours have built sufficiently capabilities to target PRC cost free, but it won't be in short/medium term.