New sprockets on a half worn chain?

[Jug]

A mate had one fail on his 600 Hornet. His chain was rusty and had tight spots. I had pointed that out a few weeks prior but he didn't seem concerned as it was a sealed chain.
His went when he was riding down a motorway on his daily work commute, it broke and was ejected from the bike without causing any damage. He then got to wait on the hard shoulder for recovery while thinking about his chain care routine.

[Kata]

I'd swap out the while lot. The total cost isn't that much. The mismatch of Old chain and new sprockets will wear the whole setup faster anyway.(according to the MC press).

As for roasting, I'm not quite sure why you haven't plugged for making a new chain using diamond crystals and graphite with your skills....

[royb]

Last year I detected a clicking noise from the chain under first gear load.
It turned out to be a worn joining link; I understand they are a softer material to allow the link to be peened, and therefore prone to more wear.

I've kept the old chain and might just measure it as per "jug" to see the wear rate of this spare.