I'm assuming the post is saying the Cowboys would free up $40 mil a year, or actually about $38.75 if contracts for both stayed the same, and with that the Cowboys could sign free agents that would build this team to a SB contender.
Problem with that plan is that top free agents cost a lot. This team would need somebody like the following to be able to compete for a SB:
Aaron Donald.
Myles Garrett.
Jalen Ramsey.
Harrison Smith.
Ronnie Stanley.
Joe Thuney.
Corey Linsley.
Travis Kelce.
Now you wouldn't necessarily need all of them, Cowboys already have one of the best guards in football in Martin, e.g. Though there are two guards on the line vs. one center, two heads are better than one!).
But the players above have average yearly salaries totaling something like (if I didn't miss one) $120 million, or an average of about $15 mil. So you could get about 3 of those players with your $40 mil.
Are 3 top players, 2 offense and 1 defense, or vice versa, making this team a top contender?
Doubt it. So nice thought, but it'd be rather pointless, probably end up like we are now - 1 playoff win every 6-8 years or so....