Reinstalling a deleted app on my iPad with iOS 6
Open App Store. 
click updates 
select Purchased 
change the tab from All to Not on This iPad


If it has been deleted it should have the cloud with the down arrow.
If it just says open, it could be that you haven't deleted it yet.... try swiping to the far left and using search... search for the app.
If you are having issues, turn off your ipad and back on again by holding down the power button then swipping to turn it off.