BHP could abort the the proposed takeover, wait for OZL's share price to fall, then buy on market. This way BHP would save money.
Another way is to buy off market at a nominated share price. Then you would know what the shareholders plan to do. Positive would sell, the negative would hold.
IN MY OWN OPINION OZL is not worth $28.25. Over valued due only to coppers resent highs.