A choke from full guard can surprise your opponent. Often people would allow easy grip access to their collar. Professor Jean Vandensteen also maintains sleeve control which makes the technique look like an armbar entry and prevents the other person from using it for defense purposes.
You can use your imagination and see the other possibilities if the choke fails. As long as you have your opponent’s sleeve, you can attempt a transition to a triangle, sweep or armbar.
To defend this attack, never allow anyone to grab your collar or sleeves. No, grip equals no offense, so always focus on grip fighting.