If Downie can be signed for a reasonable deal, he stays. If he plays well and looks like he could get a 4-5 million dollar deal, he probably goes.
McGinn stays if Downie goes, no question, but if Downie gets extended, decent odds of McGinn being traded in a package for a D man.
Between them, Downie is the more physical of the two, which probably gives him an edge over McGinn in staying with the Avs long term.
The 3rd alternative is if Stastny or O'Reilly are traded, the odds of Downie and McGinn both staying are very good. There are not really any players in the system that are projecting to jump into the top 3 lines for sure next year, so the Avs are not in any rush to shake up the depth on the wings. The only guys that MIGHT jump into the top 3 lines are both centers in Malone and Heard, and odds are those to guys both compete for the 4th line spot more than the 3rd line.