Most neglected part of the bike. I am always surprised when people ask about performance items when stuff like chains get neglected.
If the chain is in poor condition you could loose as much as 10 percent of your rear wheel horsepower or corresponding fuel consumption.
If you have siezed links. Even one. Chain is f@cked, simple as that. That siezed link may snap causing god knows what. At the very least your sprockets, output shaft bearing and wheelbearings are suffering. As well as yourself with high frequency vibration.
For the cost it works out cheaper to bin the chain and sprockets as soon as significant wear is apparent.
No reason not to get 10k from a prop maintained chain. On my old 600 i managed 18k. It was practically falling off the sprockets by then though.