Sometimes plans just don't work out.

I bought a ticket a while back on United from PIT through IAH to SAT for a meeting in SAT. I was then going to drive from SAT back to IAH for another set of meetings and fly out of IAH on US Airways to get home. Today I found out that my SAT meeting was canceled but I still have to have my Houston meetings. Normally I know I would have to re-book because I would not have taken my IAH->SAT leg and the airline would have viewed my trip as having a hidden-city and canceled the rest of my trip.

However...Seeing as how my trip is on two different airlines, I was curious to know if this changed anything about what might happen? The background on my ticket is that it is not a code share and has two confirmation numbers but only one ticket number (United stock). Is this something I have a shot at getting away with or will they just void out my return leg? The prices have gone way up since I booked so I am really trying to avoid a re-purchase. I guess I could buy a one-way out of IAH to get home but I was hoping not to have to spend any more money.

Any advice or assistance would be greatly appreciated.

Sincerely,
sH