Is this a grammatically sound sentence?

Solution 1:

There are several combined but logically sequential thoughts in the sentence. I find it clear and unambiguous so suggest it is acceptable.

I add my annotations {so}:

Seeing him defenceless

{Krishna sees that Arjuna is defenceless},

recognising that this is the only moment when Karna could be killed

{Krishna sees that this is the only opportunity for Arjuna to kill Karna},

which {opportunity},

if {it, the opportunity, is not taken } allowed to pass, would mean that Arjuna would lose the duel

{the loss being conditional on missing the only opportunity to win},

{Consequently and finally, in view of all the foregoing points}

Krishna urges Arjuna to shoot an arrow at Karna

{so that Arjuna may win}.