Am I entitled to claim the remaining amount based on the agreement which stipulated a guarantee of capital recovery in case of loss, especially after the debtor has become well-off and refuses to pay, claiming that it is my share of the loss?

The questioner is entitled to a share of the profit when it materializes, and must bear the loss if it occurs; as the Prophet, peace and blessings be upon him, said: "Gain is in proportion to liability for loss." If a loss occurs without negligence on the part of the agent (mudarib), then the capital owner is only entitled to what remains of his capital. If the loss is less than that, he may demand the difference.