Does the partner have the right to demand the full amount of his capital after the company's loss due to the Coronavirus pandemic, and refuse to divide the proceeds from the sale of the losing company equally?

The hand of both the mudarib (managing partner) and the shareek (partner) is a hand of trust (amanah), so neither is liable for guaranteeing anything unless there is an act of transgression (ta'addi) or negligence (tafreeṭ). This is based on the Prophet's (peace be upon him) saying: "The rule regarding trusts is that they are not guaranteed unless there is transgression or shortcoming." As for losses in a capital partnership, they are borne by all partners proportionally to their capital contributions. However, in mudarabah, the entire loss is borne by the capital provider, and the mudarib loses their effort.