In our group, when we're playing to win the match, once it becomes impossible for a team to win the match (e.g. 11-4 and only 5 rounds left), we just change map.
It would be nice, for those who don't like to keep playing once they can't win, to have a dvar to end the match once a certain round-won treshold is met, for both S&D and Sabotage.
This feature is actually present in a promod version developed for iw4x, promodlive 3.3 r190, where there's a dvar called setDvar( "scr_sd_winlimit", 12 ); //[0->] (rounds) that literally does this. I don't know if it's possible to port it to cod4 promod, I attached the mod files if somehow someone wants to take a look at this.
promodlive_v3.3_r190.zip