All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
That item is not forbidden for that employee and it is permissible for him to buy it and benefit from it in any permissible way.
However, what he did during his work like going out without valid permission is forbidden and his salary for that day is only lawful according to his work on that day, unless the person who is entitled to forgive him may forgive him or that he can be forgiven according to the law [terms and conditions] of the employer.
In any case, he should repent from his negligence in his official work. For more benefit, please refer to Fatwa 131474.
Allaah Knows best.