These are the answers we received from the offices of the grand maraje’ regarding your question:
The office of the Grand Ayatullah Sistani:
One cannot violate a definite ruling of Islam on which a consensus amongst all Muslims exists for such reasons and excuses and not observe the hijab and show up in front of non-mahrams without it.
The office of Ayatullah Hadavi:
Observing the hijab is obligatory under all circumstances, unless a danger threatens one’s life, wealth or dignity because of it. It should be kept in mind that observing Allah's (swt) boundaries brings about His blessing and favor, and through depending on and trusting in Him, problems are easily solved, Inshallah.
For further information, you can see:
1- Hijab in Islam, Question 431 (website: 459).
2- The reason for the hijab of women, Question 825 (website: 884).
3- Not observing hijab to avoid being accused as a terrorist, Question 1748 (website: 3125).
4- The ruling of hijab and the reasons for reinforcing it, Question 1174 (website: 1177).
5- The effect of social standards on hijab, Question 3439 (website: 4132).
6- Exceptions for the hijab, Question 5952 (website: 6614).
7- The hijab of women while praying, Question 693 (website: 741).
8- Remaining firm in faith and belief, Question 1812 (website: 3204).
9- Working in an environment where alcohol is served, Question 9779 (website: 9787).