About Sprints
Sprints should not be delayed
It is my opinion that Sprints should not be delayed, as there is no real reason for that.
This is how I understand this concepts; I can be wrong. Her we go...
Sprints are snapshots in time, done normally at fixed intervals of time, to measure Speed and sometimes Accuracy.
It is not required by the Sprinters to deliver anything, nor a release is required at the end of a Sprint. Tying those requirements with Sprints is optional.
A sprint has no goal.
Planning is sorting actions. It is a serialization of a problem dependency graph, in the dimension of time: i.e. what action will be performed before what other action.
To measure the accuracy of prediction, you can complect Planning with Sprints: Select the next N elements of the plan to be completed by the time the Sprint is done, and at the end of the Sprint compare the actual number of elements of the plan done against N.
Notice the end of the Sprint is not the due date of the N selected elements of the plan. It is a piece of information that is only needed by management: developers don't need to know this value.
This is because measuring Accuracy is optional. The most important measurement Sprints provide is Speed. For this, all that is needed is to measure what happened at the end of the Sprint, and nothing else: in particular, it is not necessary to establish beforehand what amount of value is going to be delivered at the end of it.
all this I'm explaining just to say that Sprints should never be delayed, as they have not "due date" nor "deadline"; they are just snapshots to measure some kind of performance.
"Due dates", and "deadlines", are constraints imposed by other reasons: Sprints are not one of those reasons.
Finally, Sprints are popular in Agile methodologies, because Agile, being all about flexibility and quick adaptation relies heavily on information feedback. The most important source of information for Agile is the User experience, but it is not the only one: The developers' performance and their own experience during the process are the other key piece of information needed for quick pivoting.