the plant was dehidrated, the leaf is feeding the plant thats why its the one turning yellow...if you repot it to a better media and water it as needed...you will revive the plant...terminal spike doesnt mean its terminally ill...it just grew a keiki on the terminal of the plant meaning terminal as in "bus terminal" meaning the dock or a place to start...wait till the keiki develops a root and can be independent of the mother plant then cut it...as of now it has no root ... if you separate it from the mother, it can die...but if you do right by it...it will keep on blooming and producing babies