The case isn't expected to be heard until Sept 2016, with it taking up to 4 months. So lets say it ends December 2016. Then a decision is not expected for another 6 to 18 months. So that puts it out to mid 2017 to mid 2018.
The company seems very confident that they will win. But CRA, in the process here has already forced the company to pay $229 million to them in advance. I think that's bizarre and a bit draconian, but that's how it works.
So on to the risk. Personally, I think the downside has been factored in to the price already, and certainly factored into the balance sheet with the payments made to date. The issue is a known quantity...not some surprise out of left field. My personal estimate is 3/4 factored in already on the downside.
Now on the upside, I don't think a win is factored in at all. Removing this cloud will have a positive effect, and certainly retrieving money paid is a VERY nice plus. The pop in share price would be quite strong I would think.