Are we sure the right of first refusal is BS. I seem to remember that being a huge sticking point to the deal when Bunige went independent. Quick! somebody grab a nerd and glue them to the internet until we get an answer.
Edit: Ok i did it myself...I think JaggedSac is correct I don't see mention of Right of first refusal in any of the reliable sources. Most sources show MS hold an undisclosed minority share in Bungie and that after a few years Bungie would be free to develop partnerships with other publishers.