One of Sonoma County’s largest wine companies, Healdsburg-based Ascentia Wine Estates, is insolvent and on the brink of financial collapse, according to an explosive lawsuit filed by one of the company’s owners. W.J. Deutsch & Sons, the powerful White Plains, N.Y. wine sales and marketing company, filed the suit last week in Delaware, where Ascentia is incorporated.The complaint, with allegations of fraud and mismanagement, threatens to undermine the young wine company at a crucial time as it works to build its own sales and marketing team following a break-up with W.J. Deutsch two weeks ago.