'Mirror' defines how the profile works once it starts (it deletes 'orphans' on the side you set it to do so). It has no relevance to whether the profile can start or not (re Destination reachability or anything else) nor how you try to achieve that start.
Given that you can Schedule a Mirror profile, I actually don't understand the question as phrased, and it suggests there's maybe something you don't understand also, unless it was just 'a slip of the brain'. Mirror is not an alternative to Scheduled. One is a set of rules, the other is one way to start running the profile containing them (to start invoking them)...
But yes, Silently Fail will kick in however you try to start a profile, if the side in question is unreachable, the option is set and you try (or the Scheduler tries, or anything else tries) to run the profile.
Given that you can Schedule a Mirror profile, I actually don't understand the question as phrased, and it suggests there's maybe something you don't understand also, unless it was just 'a slip of the brain'. Mirror is not an alternative to Scheduled. One is a set of rules, the other is one way to start running the profile containing them (to start invoking them)...
But yes, Silently Fail will kick in however you try to start a profile, if the side in question is unreachable, the option is set and you try (or the Scheduler tries, or anything else tries) to run the profile.