"All procedures were followed" and yet UA is in this mess after a 69 year old customer got knocked unconscious on their plane. Maybe there is something wrong with the procedures then? I've noticed a tendency for airline employees, in person and online, to hide behind procedures as a shield when anything goes wrong.
There are numerous ways this could have been prevented:
1) Keep offering more money until someone bites. At some point someone will think it's worthwhile to give up their seat. Let the free market dictate how much it's worth. However, numerous eye witness accounts state that UA offered $800 (not $1000) ONCE and then started to IDB people. A passenger even offered to give up his seat for $1600 but was refused. So, put another way, for $1600 UA could have avoided this whole mess. That's a huge mess up.
2) Fly the crew somewhere close to Louisville and then drive them the rest of the way in a cab/van/bus. There are numerous airports within a 1-2 hour drive that had flights leaving O'hare later that day, per airliners.net. This would take some coordination and a bit more $$$ - I can see why the gate agent would much rather call the cops than try to work it out.
3) Cancel/delay the next day's flight until they can get crew for it. It sucks for those passengers, but it is UA's responsibility to have crew for its flights, not the poor doctor who got knocked unconscious.