I definitely wouldn't write anything off.
But I don't feel like buying a publisher is Sony's priority. I think the biggest reason why Sony would, would be more so to prevent someone else from acquiring their partners. Especially something like Final Fantasy being acquired by Microsoft. (I think chances are good, MS will either acquire a Japanese publisher or at the very least will acquire several Japanese developers. Variety is an important aspect of their current business model.)
I think Sony has been pretty content with buying smaller developers and raising them up that way. For a tiny, tiny fraction of what some of these publishers cost, Sony has gotten some great development teams. Insomniac Games was an insanely good deal. Activision is costing 305 times what Insomniac Games cost. I think it's hard to deny the value they've gotten from buying studios full of talented people.
But I won't be surprised if that changes.
Despite Sony's history of acquisition via organic growth, I think Bungie has indicated an overall shift in their philosophy in bolstering PlayStation Studios, where smaller teams like Haven and Savage Game Studios have followed.
I just can't imagine Sony being content with acquisition via organic growth if/when the Activision Blizzard deal is cleared. If they are willing to lock up a publisher as a defensive measure, then its almost certain Square Enix or Capcom will be under the PlayStation label by the end of this decade. However, I think Sony will be the first one to make a major move in Japan, even if it ends up being a smaller purchase like Sega.