"I didn't get a rocktorate because I can shred on the guitar like no-pony else". ~Maud pie
So... a new episode... And I made a thing from it.
Turns out, Rarity is the one that shreds on the guitar like no-pony else.
So... Either Applejacks parents are dead, or the MLP staff is wrong.
The most resent episode makes it clear that they are gone, and the line "They left us something to remember them by" makes it very clear in my mind that they are never going to come back.