"Question:  Does Zenith automatically get 12% off the top in any buyout scenario?  The rest would then presumably be split on a fully diluted share basis.......I think currently about 250M shares, yes?"

Not automatically 12%. I think it depends on the buyout price. If more than US $5 billion, then yes 12%. See here.

"The Royalty Preferred Shares entitle Zenith to cumulative preferential dividends in an amount ranging from 6% to 12% of Net Apo Revenue during any year, subject to an adjustment for tax payable on the dividend. The dividend amount is calculated based on 6% of Net Apo Revenue of up to US$1 billion, 8% of Net Apo Revenue of between US$1 billion and US$2 billion, 10% of Net Apo Revenue between US$2 billion and US$5 billion and 12% of Net Apo Revenue in excess of US$5 billion."

BDAZ