Is the shareholder's receipt of his profits and principal considered as the liquidator's ownership of a share instead of the share that exited, and how is Zakat calculated after the elapse of a Hawl, knowing that the principal did not reach the Nisab at the beginning of the trade?

The described scenario is a valid Mudarabah (profit-sharing) arrangement. There is no impediment for one worker to perform Mudarabah for two or more individuals, and to combine their funds with their consent or by common practice. Mudarabah is a permissible and non-temporary contract, and the capital owner has the right to request their capital and profit under certain conditions. Consequently, the capital owner is entitled to the capital they provided and its profits. The worker is only entitled to the profits stipulated by the two partners at the inception of the partnership, and they are not permitted to consider their profits as capital unless the capital owner agrees.