Just got off the phone with FreedomPop. They told me there are no specific timeframes for WiMax going away at this time. They have no specific plans for what they will do with customers should it go away in 2015 since they aren't aware it's going away in 2015.
I'm not sure if this is correct or not, but that's what the call center guy said. I suppose in a worst case scenario I'd have to buy another one for $100 or so once WiMax goes away and I'd still be money ahead.