
For quite a long time, the scrum guide has mentioned that “A Sprint could be cancelled if the Sprint Goal becomes obsolete. Only the Product Owner has the authority to cancel the Sprint.”
However, it is unclear what a cancelled sprint is, exactly, and what happens after you cancel a sprint.
Do you just ride out the alotted time with ad hoc work, immediately schedule an ad hoc sprint planning and start a new sprint halfway or renegotiate the sprint goal and continue in the sprint rhythm that has probably been a result of agenda alignment within the team and between the team and their stakeholders?

This is left out (I think) to limit its prescriptiveness to allow for self-management; it leaves it up to the Scrum Team to self-manage how to do this, given what’s right in their context. What to do simply depends. It’s generally considered a good idea to reconvene at Sprint Planning to establish a new goal, perhaps preceded with a Retrospective.
In any case the Scrum Guide consults us to adapt when we learn something new.
“The adjustment must be made as soon as possible to minimize further deviation. Adaptation becomes more difficult when the people involved are not empowered or self-managing. A Scrum Team is expected to adapt the moment it learns anything new through inspection.” -SG

It should be 100% clear, what cancellation means: STOP IT. And it is 100% clear, what it is: the Sprint goal is not relevant anymore.
And what any organization will do then, should be 100% up to them! Some would immediately plan the next Sprint. Others might get reorganized first etc.
At the same time, hardly any practitioner I meet has ever been confronted with such a situation at all.
When lookign for detailed advise, just consult the official Scrum Patterns, see Jeff Sutherland’s “Emergency Procedure” (http://scrumbook.org/product-organization-pattern-language/emergency-procedure.html).
But please keep the Scrum Guide clean from any of these details!

There are too many possibilities what may happen after a Sprint is cancelled. Collective intelligence should come into play here. When a Sprint is cancelled it is also possible because the company is bankrupt (I have seen this). In that scenario, there isn’t even any more Sprints in the future. :D

This a tricky one. I think that if the sprint is canceled due to irrelevant sprint goal a new goal can continue the sprint #opinion

The Scrum guide states
“A Sprint could be cancelled if the Sprint Goal becomes obsolete. Only the Product Owner has the authority to cancel the Sprint.”
Scrum defines the what to do … i.e. if your goal becomes obsolete, continuing work is pointless. Cancel the sprint and it falls under the product owner accountablity (the person that is accountable to maximisng value ).
How you go about it …. that is up to the Scrum Team as there are many different scenarios. e.g. One team, many teams, cadences.
Some teams may go back and revert the work and replan. Others may immediatly call a review, retro and sprint planning.
I think the guide is clear enough on what to do and it does not cross the line of telling you how to do it. That is on the context of that work, that tam and that organisation.