PGA will not tear down Grizzly anytime soon, it still gets good ridership. PGA Is very landlocked, but they do have a few options.
As EBL mentioned, the park is stuck @ a 225 Ft Height Limit due to the route of the airport going directly over the park.
I would love to see a small hyper go in behind Xtreme Skyflyer and near the Imax. Really no need to remove any other coaster, you could easily fit a station back there, and a nice length coaster that stretched all the way back towards Grizzly.
-RD