Overheating vs oil starvation

[exponent]

I had a recent problem with a Honda Xr600R. To make a long story short the bike became harder and harder to start. Finally it was a no go. I took the bike to a mechanic who found the badly worn parts and then we discovered that the oil flow to the head was almost nonexistent. What was damaged was the rocker arm/cam-riding surface, they were worn down to almost nothing. We discovered that the oil pump had failed. Now when it came time for me to get a refund on the deposit on the bike the other party claimed I had overheated the engine and as such he wasnt going to give me back a big chunk of change. The bike was never overheated at any time but the other party claims I must prove this to him.

I've received some comments from other boards but I wont post here because I dont want to be accused of tainting the results.

The 2500 dollar question is
If the bike was overheated what other damage should have been observed?

Any help here is greatly appreciated.