My question involves estate proceedings in the state of: New Jersey

A person selling a motorcycle receives 700 of the $1000.00 price so it remains until paid in full. Before the final payment is made the seller passes away. This is 1 1/2 years ago, the guy wasn't married (son from prior marriage) and had a live in girl friend. The buyer asks the GF about the bike but she can't find the title the buyer can't produce the receipt of down payment. Without the receipt she appears to have no issues but has yet to do anything. I learned his estate wasn't probated which was a $1000.00 bike & a $25,000.00 car.
They are well past the timing to open an estate as the son wasn't aware what probate is plus no will was available. I know the bike is an asset but can that sale still be completed & transferred to the buyer? Would DMV just need a D/C to transfer or do they need to go thru probate. Other possible assets were minimal, 5k maybe; however there was a 1/2 life ins for the son. Any ideas, experiences esp when probate wasn't ever done. Could the GF have done the probate without the son's knowledge?
Thanks in advance for your input.