Unless consumer spending goes up significantly (also possible, and also good for the economy), the actual funds will likely get rolled into other investments after paying taxes, though. That's what I did after inheriting my dad's IRA: I didn't need the money, so it came out as an RMD and then went straight back into a different investment account.

I guess it could also go toward the down payment of a house, inflating the housing market even more. If lots of old people die the stock of houses on the market should go way up though, somewhat blunting the impact of this.