So even DD's are not safe
Well i have discussed it with a friend in treasury, he informed that different bank's follow different procedures, but it is possible that the DD is honored even if NOSTRO is closed. For this purpose, the bank needs to pass certain instructions/follow certain procedures. Therefore, tell your bank that replacement of DD is not a possibility but they should ensure that JP Morgan honor's the DD till its validity of 6 months. Although, such procedure may have to follow longer path of it is not presented by CIC during its validity period but have faith in Allah and tell your bank that replacement is not the option and they have to ensure that proper required corrective measures are taken.
As per my knowledge, and confirmed by my friend, usually banks have "cooling off period" in which it stops issuing new DD's but keep the NOSTRO operational for 3-6 months till expiry of validity/encashment of all pending payments. Seemingly, your banker is opting for easier way out by offering u replacement. Lemme know the local bank name, i have few friends in treasury.