Judging from the FAA airworthiness directive which TonyT linked to in another thread a couple of days ago, they could hardly do anything other than ground SallyB.  As the spar on airframe that gave rise to all this appears from the inspection done to be quite lterally coming apart, I think the tone in which the operator of SallyB seems to be keen to play down the seriousness of it is perhaps misplaced. 

FAA have stated that existing inspection procedures are insufficient to detect the cracking that has been found in the wing terminal-to-spar chord joints, and have specified the revised inspection procedures and areas to be examined.  I would think that SallyB has been previously examined under the existing inspection requirements, and may need to be examined under the newly specified procedures before her operators can be be quite so assured that their airframe is not adversely affected.  FAA have estimated the cost to US operators of doing the specified investigation and inspection work, and reporting back to them as being approaching $40k, and that is without any subsequent remedial work (the extent of which is not yet specified and will be decided after the FAA recieve the inspection reports back from the US operators). 

I would say the future for flying B17s is currently looking uncertain, and could involve some very expensive engineering work.