Ejecting at 1000 knots means ejection into supersonic flow. Not even the Zvezda K-36, the indisputably best ejection seat around, is rated for that. For this kind of speed, whole enclosures have been designed which did not work all too well when they had to be used.
For training, there are simulators to prepare pilots for that hopefully rare occurrence (the picture above is from this link; there you'll find more pics and a list of their customers), but mostly, simulations are run with simulated pilots, too. The spinal loads are too high to have pilots exposed to them regularly without the benefits which go with a successful ejection.
For the things that might happen, see what William Rankin went through on July 26, 1959. It can last quite a while, too. In his case 40 minutes.
By the way, ejection seats started to save pilot's lives in 1942 (Germany) and 1945 (Sweden).