Does Istikhara stop after one feels reassured about the engagement and before the marriage is finalized, or does one continue it due to the possibility of new developments?

Many scholars have explicitly stated the permissibility of repeating the Istikhara prayer if the matter has not been settled and the one performing Istikhara has not yet firmly decided on one of the two options. If their heart is not at ease with anything, it is recommended to repeat the prayer and supplication, repeating it until their heart is at ease. Some scholars have cited the permissibility of repeating Istikhara by considering it a supplication, and it is permissible to be persistent and repetitive in supplication. They supported this with the action of Abdullah ibn Al-Zubayr and by the fact that the Prophet (peace be upon him) used to supplicate three times when he made a dua.

In summary: There is no harm in repeating Istikhara as long as the person praying is hesitant and has not made up their mind. However, if their heart becomes at ease with something or they have made a firm decision, they should not repeat Istikhara. As for engagement and marriage, one Istikhara is sufficient for the engagement, as it is a prelude to marriage. If the engagement proceeds and the soul is at peace with acceptance, it is not prescribed to repeat Istikhara, but rather to rely on Allah after making a firm decision.