You're not entitled to the cost of a new replacement- just as if you were driving a 1987 car, you would not be entitled to the value of a new 2013 if someone totalled it. You're entitled to the market value of the bike you lost, or it's repair cost. Market value can sometimes be proven by what similar bikes have actually sold for on Ebay. And of course you are entitled to reimbursement of all other expenses/losses associated with the accident.
I was in one [car] accident in my life. I wasn't hurt (even though my head went through the side window- us Eye-talians have hard heads!]- all IO wanted was fair value for my totalled truck. Insurance co. made a RIDICULOUS and insulting offer and nothing more. I suddenly found myself going to a doctor. I never lied or said anything that wasn't true; never faked anything/ never insinuated anything...just went to the doctor, and let him do his thing and state his findings. I ended up with several times the valuer of my truck, after the lawyer's cut and doctors bills...... Sometimes you have to play hardball with these creeps if they refuse to be fair and accept their responsibilities. Had they merely given me the fair market value of my truck, I would have gone away and they would have saved a lot of money.