Thank you very much for this detailed reply.
I understand your point about wear and tear on the sprocket, and how it is a good idea to have the amount of wear and tear to be equivalent on both sprocket and chain so they both reach their end of life together.
However, I have a Honda 125 Deluxe of 2011, and it has only 2000 kms on it. I work from home, don't drive it much, and for only short distances to the shops. So in 5 years, I've only driven it 2000 kilometers.
I believe The chain link broke because the chain was rubbing up against the chain cover which was slightly bent inwards maybe because of a kick or dent, which I had fixed by getting the chain cover fixed and the chain tightened up a bit.
Having read the above, would you still recommend I get the full chain and sprocket set?
Thanks again for your help.