What is the ruling on zakat for money accumulated over ten years under the mentioned circumstances, and is zakat obligatory on borrowed money that has not been repaid?

The fundamental principle is that Zakat becomes obligatory on money if it reaches the nisab and a full lunar year (hawl) passes over it, whether it is intended for marriage, purchasing furniture, or anything else. However, if it does not reach the nisab due to spending, then no Zakat is due on it. The enquirer should review their accounts and verify. If there is doubt regarding the obligation of Zakat, the fundamental principle is that it is not obligatory.