Does a partner in a project that was halted, and whose money was used personally, deserve a return or compensation, or is his right limited to the principal amount that has not yet been repaid?

If the contract was a valid Mudarabah (profit shared equally between you, and no guarantee for the capital), then any profit you received is yours. However, since you betrayed the trust and disposed of the money for yourself, you are a usurper and must return the capital and your share of the profit.

However, if the contract was an invalid Mudarabah (based on a fixed amount, or a percentage of the capital, or with a condition to guarantee the capital), then you are obliged to return the entire capital with its profits to its owner, and you are entitled to a fair wage for your work during the Mudarabah period. After you disposed of the money for yourself, you are obliged to return all the disposed money in addition to the received profits, deducting from it your fair wage.

Ibn Qudamah says regarding an invalid Mudarabah: "All profit belongs to the owner of the capital, because it is the growth of his money. The worker is only entitled [to profit] by the condition [of the contract]. If the Mudarabah is invalid, the condition becomes invalid, and thus he is not entitled to anything from it, but he is entitled to a fair wage."