What about the marriage if it was proved that the husband is mentally insane and he did try to kill a woman in a supermarket and now he is in a hospital for the insane?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

According to the majority of Muslim scholars (and the four Imams are among them), madness for some time or all times constitutes a genuine defect that gives the choice to a spouse (husband and wife) to revoke the contract of marriage even though such state of madness takes place once a month and it produces harm in any form, whether it is before or after making the contract of marriage.
As for madness that does not cause a harm as one who falls down on the ground and then regains his/her consciousness without any harm, such a case has no effect on the contract of marriage unless it is proved that the spouse knew it before entering the contract.
Thus, if what this woman mentioned about the man is correct, then the wife has the right to choose between revocation of the marriage contract or keeping it and staying with her husband.
Allah knows best.