Is it permissible for my sponsor to stop sending me money so long as I can cover my expenses by working, and is that considered a breach of the sponsorship agreement?

It is obligatory to adhere to the agreement with the competent authority regarding the presence of a financial guarantor to cover tuition fees. However, if the authority permits working during studies, you may work and cover your tuition fees yourself. In this case, the guarantor is not obliged to send a monthly amount, as long as the authority aims to ensure regular payment of expenses. The condition of a guarantor remains binding, even if symbolic, based on the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions concerning what is permissible."