Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions.
This is not considered as a necessity which permits you to take an interest loan because Allah the Exalted says: “And if the debtor is in a hard time (has no money), Then grant Him time till it is easy for Him to repay.” [al-Baqara: 280]. It is not obligatory upon you to return that money using a prohibited way, but rather the creditor should bear patience till it becomes easy for you to repay. There are scholars who said that necessity does not permit interest. However from what is apparent to me, interest is just like any other unlawful thing but it should be known that necessity does not permit an unlawful thing except under two conditions:
First: It should be unavoidable to engage in the prohibited thing so as to avoid harm.
Second: It should be certain that the impermissible thing will eliminate the necessity.
However, Istikhara is not performed for doing an obligatory act or leaving an unlawful or detested act because its purpose is to seek the best from two choices. An unlawful thing must be avoided and there is no better option than doing that, because there is nothing better that is unknown in an unlawful thing compared to the bad that is in it. Nonetheless, Istikharah is permissible if it is meant for deciding on an unlawful thing or choosing between two unlawful when they become permissible due to availability of necessity that permits forbidden things.
And Allah knows best.