"What was the name of that Mantra, Guru Dev?"
Karna was sure that it was Indra who made all that happen, Though it is also possible that the Niyati could not allow someone that powerful to exist in the mortal realm but in either case, Indra is directly responsible for it.
But Karna was more curious about the Mantra, If he get that mantra, He didn't have to worry about the safety of the people around him, that way no one can use his people against him.
"Name? What else it could be other than Sanjeevani Mantra, It's given to Asura Guru Shukracharya by Lord Shiva, Which he passed down to Maharishi Dadhichi.
That is one of the few things that can defy death, Hence why it looked so highly off, And the reason why it is given by Lord Shiva, A Mrityunjaya (Conquer Of Death)."