Company A buys Company B''s assets. Company B no longer operates, but had outstanding potential contractual debts. Is A liable for B''s debts?

As with most answers from a lawyer, I must preface this answer with, "it all depends."  The basic rule is that the obligations of a business do not follow the assets.  There are exceptions.  If the price paid was not "reasonably equivalent" to the value of the assets, the sale can be unwound as a fraudulent conveyance.  This is true, even if there was no intent to harm anyone.  It is enough that that the price was inadequate.  The price, however, takes into consideration the problems the business was having.  There are also some exceptions for particular kinds of debts.  Pensions, union contracts, and a few other particular obligations pose separate problems.  The detail in the bill of sale is another issue.  It sounds like these wee attended to.  Normally I would start by looking at the sales contract and the bill of sale.  I would look to see if it included an assignment of the phone number, etc., Also, the old employees were "re-hired." Did the employees give new I-9s. W-4's etc?   Also, is there any carry over in the payroll?  Did the old business file final tax returns? Was the lease assigned?  Is it operating from a new place of business?  Was the customer list sold?  Were some of the old debts paid by the new company? What about existing contracts?  If all of those things are in order, and from your question, it seems they probably were, then I don't think the creditor has an easy task.  If you want someone to review it in more detail, we can do it, for no fee, and with no obligation.