Hi confuse mind,
Do you mean that the pronoun in the following sentence is ambigious
Ram killed Shyam and he will marry his daughter now.
I feel that he is not ambigious while his is since subject of second part wil refer to the subject of first part.
Hmm... I would actually argue that both the
he and the
his ARE ambiguous, grammatically speaking, in your sentence.
The thing is, we've got two independent clauses (i.e. two phrases each of which COULD stand alone as a complete sentence):
(1)
Ram killed Shyam.
(2)
He will marry his daughter now.
If we choose to join these two sentences into one with a conjunction, we've formed a true compound sentence, and whenever you form a true compound sentence, you need a comma before the conjunction. (That's also, incidentally, why the OG says that the original sentence in question here creates a run-on, though to me the pronoun issue is the bigger problem with it -- and the easier one to spot, since pronouns are grammar-based whereas run-ons are more punctuation-based.) So if we're going to retain those two sentences and just join them, we're
required to revise to
Ram killed Shyam, and he will marry his daughter now.
But once that comma intervenes to separate the two clauses fully, I don't think the "he" of our second independent clause is under any obligation to link to the subject of our first independent clause. (After all, the clauses are independent.) It might link to the subject or the object.
It's true that strictly semantically, the referent of that "he" is probably clear, since dead people don't marry people. But we've depended on the meaning -- not the grammar -- for that clarity. Furthermore, if this were mythological or something, dead people still probably could marry people!
Consider the following two sentences:
Sarah passed the phone to Laura because she couldn't bring herself to speak.
Sarah passed the phone to Laura, but she couldn't bring herself to speak.
I'd say that meaning-wise, it's clear that the "she" of the first refers to our subject Sarah and that the "she" of the second refers to our object Laura. This suggests that the "she" has the flexibility to point to either of the girls, though, and strictly grammar-wise I don't think the referent is clear in either sentence.
So it seems to me that the best way to revise the Ram/Shyam sentence to be safely clear in terms of its grammar is to take out that pronoun "he," because then (a) there's no need for a comma and (b) "will marry" will share the subject ("Ram") established before, since no other subject intervenes and offers itself. (This subject-sharing -- when a single subject reaches out to two verbs -- is that "conjunctiveness" the OG referred to.

) You'd still have ambiguity going on with the "his," though, as you say.