Typically, when a dominant offense faces a dominant defense, more often than not, the defense will win out- it does win championships.

But nothing lasts forever, plus there have been some exceptions to this rule:

The Edmonton Oiler dynasty of the 1980s
1999 Rams
Nebraska's 1995 National Champions
Florida's 1996 National Champions
Miami in 2001

The evidence of prolific offense not being able to win it all is pretty damning- 2007 Patriots, Oklahoma football last year, 2001 Rams, 2002 Raiders, Air-Coryell Chargers, etc.

Someday, do you think it'll ever happen?

Will there come a day when someone can silence the "defense wins championships" mantra, or will it go on forever?

Not likely. The offenses with the teams you mentioned were so dominant, it didn't matter how much D they played. There's no team in any sport today that could do it. The Suns were screwed once they played the Spurs. The Warriors can't even make the playoffs. The Patriots lost to the Giants. The Yankees lose year in and year out. The Red Wings have only won the Cup once since 2003 and the Senators always lose in the playoffs.

The only way this can happen is if the offense is extremely dominant and there is no team today that is that dominant offensively, not even the Patriots.

The Best example, 2007 Super Bowl

Pats were 16-0 and had a dynamic offense, and went 16-1 LOL

of course it was to the giants who I hate, but it showed that a great defense and getting pressure on the QB, any QB, wins football games, and the most important ones too.