My opinion, is that you need Mario if this is the case.
Now if Reed & Barwin have double digit sacks & we aren't blitzing as much..... Then I'll be fine with letting Mario walk.
For years, Mario has been the best player on defense, with no help. We started this year, & everyone across the line was getting sacks. JJ Watt, Barwin, Antonio, Mario & even Cody.
When all those guys are involved with pressuring the QB (& I know sacks aren't the end all be all, but if you're getting sacks, you're getting hurries, pressures, & hits). Then you've got something.
If at the end of the year, Brooks is the only one with double digit sacks, & no one else is close, then it doesn't make sense to me to not bring Mario back.