I have heard used jumping to (the worst) conclusions, even when the process was not a simple deduction. But your examples (especially the first) are more applications of the appeal to extremes fallacy:
Description: Erroneously attempting to make a reasonable argument into an absurd one, by taking the argument to the extremes.
This can also be done for dismissal purposes, and in that case is more resemblant of a reductio ad absurdum (except that the absurd consequence is not at all inevitable, and that's why the attempt is "erroneous"): "You don't want to stop for lunch now? Sure, let's all starve".
If the consequence is not (as it is in the first example) of the actor's doing, but is feared by the latter to be a consequence of the other party's actions ("if you do that, we'll all die horribly!"), then it would be alarmism. Your third example is more like this.
In your second example, it could also be a case of overreaction.
- to react or respond more strongly than is necessary or appropriate.