Depends on the terms.You'll own a smaller % of the combined...

Depends on the terms.
You'll own a smaller % of the combined business but it'll be worth more.

BHP should have a strategy whereby they sell off the parts they don't want for higher than book value + goodwill so that the net cost of the remaining assets is less than their value going forward. Use the cash proceeds to either reduce debt or pay for capex.

As always it depends on the price they pay.
The market movement on Friday should tell you whether it's likely to be a good deal or not.
Just remember BHP tried to buy RIO at the peak of the commodities boom pre GFC, plus they spent big on shale assets only later to sell them for a massive loss.
So BHP don't exactly have a good track record on acquisitions.

It'll be interesting to watch.