You should report on your return what really happened. Having said that if you know there is a correction coming you should wait; it may save you an amendment down the road if something besides box 16 information changes.
Whether or not you get a corrected W2 the allocations come from your box 1 wages and the work time in each state. So that should not change (unless the correction is to box 1).
There is nothing extra necessary to send in with your returns. Keep a record of your calculations/allocations in the unlikely event that it comes up in the future. As long as your method is a reasonable/logical method you will be good to go. Being on unpaid leave during the time in IN would reasonably and logically lower the percentage of total wages that belong to IN.
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