Is it permissible to uncover the face in a very hot area after having vowed to cover the face? And what are the consequences of uncovering it?

Covering a woman's face from non-mahram (definition) men is obligatory, as she is forbidden from displaying her adornment, as stated in verse 31 of Surah (definition) An-Nur. Making a vow to cover the face further emphasizes this obligation, making it obligatory both by religious law and by vow, and it is not permissible to abandon it. A Muslim must be patient in performing acts of obedience and avoiding prohibitions, and the consequence of this patience is attaining Allah's pleasure, as mentioned in Surah Al-Asr. It must be remembered that high temperatures do not permit unveiling, and the heat of Hellfire is far more intense.