A stock split fundamentally does not affect the value of a position. One would have to take into consideration the stock price after split.
If WMIH after split surges because it's fundamentally strong, and they stated that they want to attract more institutional investors , volume thus moving the price up, then in this situation a short would be in trouble.
Therefore, taking the above and other information that they have provided us, I would venture to say that covering the short before r/s is more sound of an approach.
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