You should contact him about it so he can take the steps to remove his information. It's both of your's account and you shouldn't try to sneak it out from under him so it can be fully yours. That's wrong.
50m = $100 so if it's worth more to you than that in sentimental value than keep it. Just make sure you sleep on the thought before making it a main. You would hate to have put all that work in to regret it later.
But correction - This account would probs be worth more like 15-20 mil
If you hate pking I'd say why not make it a main? But that's also a valuable account if you wanted to sell it. Up to you m8, but based off your situation I'd make it a main.
Just my opinion but I think it's only valid to have a 24hr time window for a rufund if the person will get back to you promptly. If every time you have an issue it takes 12 hrs you're screwdd from the beginning. Sounds a little dirty to me.
Update and replace your old mirror.jar with this one -http://osbot.org/forum/topic/70298-mirrorclient-v1053/
Cheers and let me know if you have anymore issues.
This is typically a problem with the actual runescape server and happens to everyone every once in a while. I don't think it's client related. Let me know if the problem is still going on.
Honestly don't think they try to back trace all that much, otherwise they could go back and look at any account that has used an injection client. I think they focus more on catching in the moment. Just my opinion from personal experience.