supreme court has held jat reservation unconstitutional on ground of sufficient data of jat population and social status of jat in the society. supreme court has not held that it's judgment [save reservation committee vs union of India] has retrospective effect and all the examinations completed before the date of judgment is unaffected from this judgment.
in your case promissory estoppel will apply and IBPS can't reject to join because if IBPS do so then whole examination is illegal because jat candidates got reservation at two stages, one at the written exam and second at final result. then the obc candidates right who had disqualify by the reservation given to jat by IBPS is affected and they are prejudiced by the IBPS.
so removing this complexity, supreme court did not give retrospective effect of its judgment. you have right to get joining. your result is unaffected from this judgment. if ibps refuse to joining , you should file writ petition before supreme court and challenge ibps final result.