I think he would have been selected. Eddie was on to a winner however he might have performed …
If he'd picked Simmonds and he'd done spectacularly well, he could have said 'now he's ready for England', but could also easily back track by adding 'but it's only against Tier 2 sides' to provide a get out for having to pick him for the AIs if he didn't want to. On the other hand, if he'd played poorly, he could have said 'see, I told you so'.
Ultimately I'm with Tigs. I think the Lions tour has pretty much confirmed that Simmonds does well in specific scenarios but not well enough elsewhere (and at the nuts and bolts of playing in the back row) to really stand out. Running riot against the USA or Canada wouldn't have put those doubts to bed, but they'd have added more fuel to the argument for involving him and probably wouldn't have exposed any reasons not to.
There's still time though … the first test hasn't even been played. If things don't go well and Gatland needs a re-think, I wouldn't be totally surprised to see Simmonds on the bench for the second test (probably with Faletau starting). If he got that kind of opportunity and showed he could be a game-changer, the Lions tour could still turn out to be the making of him as a test player.