There is nothing wrong with a woman taking off her niqab or khimar in front of a blind man.
It was narrated from Faatimah bint Qays (may Allaah be pleased with her) that the Messenger of Allaah (peace and blessings of Allaah be upon him) told her to observe her ‘iddah in the house of Umm Shareek (that was when her husband died), then he said: “She is a woman whom my companions visit. Observe your ‘iddah in the house of Ibn Umm Maktoom, for he is a blind man and you can take off your garment.” Narrated by Muslim (1480). In another report it says: “If you take off your khimar he will not see you.”
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was asked: What is the ruling on observing hijab in front of a blind teacher?
There is no hijab in front of a blind teacher because the Prophet (peace and blessings of Allaah be upon him) said to Faatimah bint Qays: “Observe your ‘iddah in the house of Ibn Umm Maktoom, for he is a blind man and you can take off your garment.” End quote.
Fataawa Noor ‘ala al-Darb by Shaykh Ibn ‘Uthaymeen (Fataawa al-Nisa’/ 170).
Shaykh Saalih al-Fawzaan said in al-Muntaqa min Fataawa al-Fawzaan (3/question no. 410):
The correct view – and Allaah knows best – is that she does not have to observe hijab in front of a blind man, i.e., covering her face in his presence. End quote.
And Allaah knows best.