Gary Johnson wouldn't get more than 1% of the vote in any state except New Mexico.
2% at best nationwide; 5% at best in any state. In likeliness, around 1% nationwide and 2% in his best state.
If Johnson: .8% - 1.1%
If Petersen: .5% - .8%
If McAfee: .5% - 1%
If Perry: .3% - .5%
Johnson will almost certainly be the nominee and will probably underperform his 2012 result.
The most I think Johnson/Weld could possibly get is 2%, and that's with David Koch accidentally shelling out a few million to help them out.