Probably. But the point is that Huddersfield have had 'massive success' already, at least comparatively, with 2 cup finals and a league title. How much more success do they want before these mystery thousands start turning up? Any potential Huddersfield spectator that is waiting on the sidelines for more than that before committing is going to be very hard to please and, I would suggest, will not keep attending if they revert to being a struggling lower mid table team.
No they certainly won't stay around for loyalties sake. Bradford have proven that and Halifax and Keighley and Featherstone. However once the upward curve begins and the team is increasingly successful they will return as is also demonstrated at Fev, Warrington, Widnes and even Leeds. Huddersfield have substantially increased their attendances since the dark days of the barracudas and the cellar dwelling SL team, but have not yet reached the top of the success curve and there is 60 years of failure to overcome.
I truly believe that if they win the GF their attendances will move towards the 8 to 10 000 level. No one can really know though. Winning the GF will be a start and we will see what happens following that.