It's not a matter of 'Dan Curtis letting them use another director. If a studio shows interest in a DS feature, there's not a chance in hell they'd let DC direct it. He has no track record directing features. The last one was 12 years ago and a flop.
He'd be lucky to have a director like Tarantino show interest in doing it and he'd be insane to say no. I doubt a studio would allow him full control over the choice of director.
If the WB wouldn't let him direct a dinky little $5M pilot, they certainly wouldn't let him direct a $50M plus feature! Especially if a star was attached.
Whether I agree or disagree on that fact is moot. Simply as a business decision, it doesn't compute.
Now, if let's say a star came aboard, like a Depp-type heavy hitter and he demanded that the studio let Curtis direct, there would be a chance it could come to pass. Or, if DC put up half the budget himself, though I doubt that would happen since he blew $3 or $4M of his own dough on GOING TO MEXICO/ME & THE KID, was burned by it and certainly won't go down that road again..