If co. goes out of business, can owner then be sued personally even though transactions were all with business only?

That depends.  Was the business a separate legal entity, such as a corporation or lllc?  If so, the owner would not be personally liable for its obligations, with some limited exceptions.  If the business entity cannot meet its obligations, an obligee may try to make the individual owners liable by attempting to "pierce the corporate veil", i.e. the obligee will argue that the corporate form should be ignored because the corporate owners either ignored the corporate form themselves (for example, commingling corporate and individual finances, using the corporation to pay individual owner's debts, etc.) or used the corporate form to defraud.  Assuming that none of those exceptions apply, you would make a motion to dismiss the claim against the individuals on the basis that the obligations belong only to the business entity.