I hope it is just theoretical for OP because vague anonymous questions are not the best way to seek advice on real-life situations.
That out of the way, here is what I think...]
The wording is a bit vague. If you mean rape, why not call it rape? And no, one does not have the right to rape his wife.
On the other hand, there is plenty of room in relationships for both partners to pressurize each other on various issues, not just sex.
What is "verbal threat"? It could mean "I will kill you", or "I will take sanyas" or "I will tell your mother/friends". We may feel differently about these "threats".
IOW, it is perhaps near the outer limits of ok to forcefully demand sex, but not ok to forcibly perform it. 😊
Seriously, so much in life depends on details: At one extreme, the couple may be having plenty of sex, but the husband is so unreasonable that he cannot take an occasional "no". I'd think, what a jerk. At the other extreme, the wife could be thinking that marriage is all about kitchen, saris, and jewelry, and the couple have no sex life to speak of. Now the guy has my sympathy.
And, as mentioned above, the "threat" in question could refer to physical harm or simply "I'll tell our friends that we never do it."
Finally, marriage is not a jail. It is ok for either partner to leave if he/she is sufficiently unhappy and unsatisfied. Of course such decisions need to be taken with careful thought, and with awareness of consequences to reputation, finances, future relationships, and other family life (eg, relationship with children).
Anyway, a thought provoking subect!