I voted 1 year, but I'd say 2 or 3, honestly.
The amount of separate components in a drive, combined with the R&D drive manufacturers dump into them getting rerouted to rebuilding, the amount of channels the platter drives fill (Retail, OEM, E-tail, Externals, DVRs, Expanding datacentres/businesses/databases, RMA requests, repairs, recovery companies, government, so on and so on), the amount of time it will take to reinstate a plant to the required level of clean to be able to make the drives, relocating, not to mention the inherent problems in Thailand itself needing to be resolved (namely disaster recovery) before most rebuilding can begin...
And after all that, WD is really going to be hurting for money, as nowadays drive manufacturers don't make a whole lot of profit per drive compared to its production cost.
Shit... 3 years, at best for normal prices...
Edit: Unless WD starts to pour more focus in SSD tech, which would be a welcome addition, and probably a path they might have to take to make enough back down the road, not to mention remain competitive with Hitachi and Seagate which didn't get hit nearly as hard...