All I've heard is that maintenance is hoping to get it reopened by next season.
Most of the rumblings I've heard about the new addition are pointing to an Endeavor going in Highland Fling's old spot. Of course, we employees really don't have any more knowledge about future additions than most people. But it makes the most sense to me- they already have a queue and ride pad just sitting there. And Fling was a family favorite, lots of guests seem upset when I tell them that it's not there any more, so I'm sure it would be a hit. Whatever ends up going there can't be much taller anyways due to Dragon's Wing flying over the area.
That is what makes the most sense to me. I loved Highland Fling and an endeavor, hopefully the higher capacity model, would be nice to plunk down in that spot. Assuming it has a lights package that many of the new ones have, it would really brighten up that area of the park at night.
Sadly six flags St. Louis doesn’t care to maintain lighting packages