First question - It depends on the orientation and diameter of the pipe vs. the cohesive tension of the fluid. If the pipe has sufficient cross-section, some water will leak out initially regardless of the slope if the pipe end is held horizontally.
Second question - The pressure will never reach the far end, because there is no pipe that has zero rigidity, and sidewall flex will take up any pressure you could possibly apply. The frozen water in the pipe at sufficient elevations would preclude it as well.
Third question - Same issue with sidewall flex, and you need to define the variable "midway" - i.e. if the leak is 13,000 miles away, or two feet away.
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