not long for this world

somebody is not long for this world (used in order to say that you do not think someone will live for very much longer) — не жилец, долго не протянет; недолго осталось

Example: Poor old dog — she is not long for this world. (Longman Idioms Dictionary)

also
one's life is not worth a day's/ an hour's purchase — и дня (или и часу)≈ не проживёт, не протянет; на ладан дышит

see
[не жилец]