The thing that's gonna kill bitcoin is the lag time between payment and confirmation. Also, the need for escrow for larger transactions.
Sometimes transactions are taking long time to complete. But you cannot say that it will destroy bitcoins. There has to be a solution to this problem and when the solution will be implement, bitcoins will rise to new heights
Delayed transaction wouldn't "destroy" bitcoin, but maybe it broke bitcoin feature that we know the fastest transaction.
Nothing can destroy bitcoin unless United Nation decide to shut down every activity realted to bitcoin .