If your finance company refuses to take back the vehicle after bankruptcy can you just leave it at the dealership?

Its done every day of the year.

No. Even if the dealership would let you,(never happen)it is still your responsibility. Apparently the lender feels they can collect the debt by other means. Secured lenders have the option of negotiation or collection of the debt in full. Bankruptcy does not relieve you of secured debt, unless it is agreed upon by the lender.