Not sure where they escaped to, but they were pretty powerful. Will we be facing off with an extremely powerful Gnoll? Will they partner with Magatha Grimtotem? Magatha still has that super powerful Twilight device from the Thousand Needles questline, right?
On a side note, would love to see this happen:
I doubt it, since Wratheye wanted to decay everything & feast upon it – Sort of like a rough humanoid version of G’huun. 
Magatha Grimtotem may be a villain of sorts, but she’s still not so delusional into siding with powers that simply want unwarranted destruction for the sake of pure destruction & nothing more — Afterall, she even helped us against the Burning Legion.
At best, I’d argue Magatha would side with Wratheye as merely a means to an end – Like a temporary pawn to further plot the ambitions of the Grimtotem & her people.
It would be a bit out-of-order for new players, but I suspect she might become the final boss of the Bel’ameth area (if it is eventually upgraded into a new starting zone)
I doubt she’ll make it to The Last Titan. Definitely not the end boss. She’ll be a raid boss somewhere along the way.
Could show up to cause chaos on the nearby night elves but Malfurion would erase them. Depending on the writer. 
Still waiting to we where Denthrius went to