I wonder will they ever release that promised sequel of Curse of the Mummy?
Not likely. As Jon mentions in his interview in issues 1 & 2 of "Fighting Fantazine", it was an old pre-Wizard Books idea. If he were to get the chance to do another FF gamebook, he'd be more likely to go with a newer idea.
"Saga of the Stormchaser" is an outside possibility since Jon had already put some of it together to pitch to Puffin, but again, from the interview, he would probably throw all that out and start from scratch again.