Could Teck just do nothing for the first 3 yrs, and buy us out in the 4th?

Not really. We'd be the controlling party making the decisions until they spend what they have to, and if they wanted to buy our share at that point they'd be paying FAR more of a premium.

OR would they then run the risk of us selling to someone else?

They would run that risk as well.

AND if we sold to someone else..... Would it still be that Teck needs to be in production from the original date of the BFS plus 120 days?

As long as everything is sold to them, the contract should transfer over as well, and anyone buying would probably want to buy with that kind of contract as well.