This story at philly.com reports on the completion on December 24, 2013 of the acquisition of the Rosenbach Library by the Free Library of Philadelphia. The state attorney general had no objection to the merger. The April 2013 story didn't go into detail about the board changes, described in this article, which suggests more of a "merger" than earlier reports.
Is it a merger of the two organizations, or an acquisition of the Rosenbach, with its collections and some of its donors, by the FLP? It seems to be both. Time will tell.
In the corporate merger of CitiCorp and Travelers Group in 1998 there was the assumption that it was a merger of equals, but time proved that to be untrue, as Travelers's corporate culture eventually changed Citi. People who worked at Citibank before and after have told me that the merged Citi became more cut-throat. I can't comment, but over time the true nature became apparent. But I'm comparing very different merger-acquisitions.I think the Rosenbach-FLP is positive and will be a good thing for both institutions and collections. Bravo to the Pew Memorial Trusts for encouraging this merger.
One speculative thought. I do not know the corporate structure of the FLP, but I wonder if the Rosenbach foundation, which the FLP will now partly control, will prove a fruitful private-public venture rather like the New York Public Library's Astor, Tilden & Lenox Trust. The NYPL is the public system (the branches) which is tax-payer supported, and the special collections (mostly endowed and mostly at 42nd Street) which relies on endowments and tax-payer subsidy. While I've never investigated the extent of support from the endowments (primarily for book purchases and some professional salaries) vs. the tax-payer support at the NYPL, I do sense great strength in the model, especially in securing additional private funds. All best wishes to the new consolidated Rosenbach and FLP. May this major change bring new energy to you scholarly and public programs!