can a BTC exchange be terminated before it has been affirmed, or is it that once communicated it is beyond the realm of imagination to expect to drop whenever
Once a transaction has been confirmed, there is no way you can reverse it. But, if it has 0 confirmation, you can try Replace-by-fee(RBF)/doubling spending by using higher amount of fee. But looks like you don't have access to your wallet, so it is nearly impossible for you to "cancel" the transaction.