Hi,
The 1.2 patch is giving us another ending, yes, but...
Only the ending "video scenes" are different from the "without the 1.2 patch" version ! It's not changing anything on the way you play the game, or other part of the game.
It's adding some scenes of Max & Nina getting out of the place and between Nina and his father (who disappear at the beginning of the game, remember!) since we did not have any news from him in the original version. And some "pretty funny" changes in the "credits"
And there is no need to re-install the game (if it's still on your computer) just install the 1.2 and keep playing till the end or if you already finish it just take back your last save game and replay it to see the new end.