The funny thing with this, is anytime the Big Show sides himself as a 'hired monster', he typically wins the Heavyweight Championship. I don't know if that's what we can expect in the future, but it's definately something to keep an eye on.
Looking back in history, Brock Lesnar's undefeated streak (and his Championship) were both taken by the Big Show, when Show sided with Heyman, turning on Lesnar. Now Big Show is siding with the Smackdown General Manager..
I fully expect the Big Show, win or lose against the Undertaker at what I assume will be a No Mercy match.. to end up facing Triple H. at Survivor Series, where he'll be likely involved in the annual "conspiracy" of the night.
As far as Taker v. Show goes, I doubt it'll be anything that goes beyond No Mercy, unless it comes to involve Edge returning, which is possible, but since Big Show was basically "promised" a Championship match.. my guess is it's a one month feud, just long enough for Show to pass time until his turn as another transitional Champion.