Also the words seem deliberate to me "...the proposal that is being made to Mosaic at 15 cents per share is final as to price."
Final as to price - therefore not final as to terms.
A very simply way for the bid to be in effect increased would be to still pay 15c for the assets but allow the cash to be returned to shareholders via a capital return or dividend arrangement. This would add about 4c per share in real terms I think.
Dazzler