You have to pick:

We'd have ten years to dig whale-bunkers and reinforce the roofs of our bigger, tougher buildings to survive the whale rain. Bad, but not unsurvivable. And we'll have a lot of whale meat to subsist on while waiting for the ecology to recover (we'll have to stockpile preservatives and the equipment for making whale jerky, or mine the vast deposit of frozen whale meat that would cover the Antarctic).

I was discussing this with some friends and one argued that the kinetic energy of that many whales hitting the earth at terminal velocity would be worse than a meteorite. It would cause tectonic shifts, volcanic eruptions (including the Yellowstone supervolcano) and a huge dust cloud that would create an unsurvivable nuclear winter.

Hm. Global earthquakes as the ground shifts and settles, and places with ground level near the 100m mark will probably get fissures spewing high-pressure liquefied whale from them. That's kind of nasty. But I wouldn't be surprised if most of the whale goo remains sequestered deep underground in the high-altitude regions and becomes a new sort of "fossil fuel" resource to tap into.

Ten years gives a lot of time to earthquake-proof our infrastructure, though it'll still really suck. Not as bad as most of the other world-affecting whale WYRs.