Is the company buying out your company responsible to honor your accrued vacation hours you have at the time of buy out? If they arent then who is the old company or is the employee out of luck?

 It depends on how the company is bought out:
1) Your company was a LLC or corporation and the buyer bought and kept the existing LLC or corporation: because the "old" company still exists, even though it has  new owner, it is still responsible for the PTO.
2) Your company was an LLC or corporation but the buyer did not purchase the LLC or corporation (instead, it bought the "assets"--the inventory, accounts receivable, intellectual property, "goodwill," etc. of the company you'd been working for, but not the actual corporate structure). In this case, the buyer is a separate legal entity or person from the company you'd worked for and is not responsible for anything the old company promised you, the same way that if you hired a friend's nanny when they no longer needed her, you would not owe her anything the friend had promised. Technically, the old LLC or corporation would owe you the PTO, but since it likely has been or is being shut down, dissolved, or liquidated, or simply has no more income coming in to pay anything, you will most likely never see that PTO or any money for it. You could try suing, but that will most likely come to nothing.
3) The old company was a d/b/a: the former owner still owes you any compensation you earned but did not receive, since you worked directly for him and he was personally obligated for your compensation, including PTO. You may be able to sue him for the value of the PTO.