Ah bummer I've had this happen before as well - 1.068 is quite high to start out with and only using a single pack of yeast is likely not enough - even for notty... Makes it worse if the packet it old and a lot of the yeast is no longer viable...
When things get stuck in the middle (like 1.030) I think there's often more than one thing going on. Not enough yeast is a good candidate, couple that with complex sugars that are harder to break down and you can get a good stuck ferment. I have also tested PH before though and found I can get things going again by raising the PH and re-pitching. If the yeast can't do it by itself you can help it by getting the PH back above 5 or 6. Bi-carb works, but Sodium Carbonate is better, Potassium Carbonate is awesome. 1 tsp per 5 gallons will raise PH by 1 point. I know brewers don't talk about PH that much but I've found it can make a difference...
Brett is pretty heavy duty and won't have any issues with finishing your beer, but be prepared it wont taste anything like Notty ferment
I'd toss in a tsp of pot-carb, re-pitch another Notty packet (or US-05 as its pretty neutral) and give it another week... I have lots of pot-carb if you want to try this approach. Great if you have a PH meter to test with... (bring a 30ml test sample to my place if you want to test it and dont have a meter).
