Is onglyza (saxagliptin) safe for long term treatment? possible pancreatitis and thyroid cancer? how to avoid pancreatitis, lactic acidosis, & ketoacidosis?

Yes, but: There are potentially serious side effects from any medication. You have listed the most serious, and rare. The key question to consider is the benefits and alternatives to this drug. Bring those concerns to your doctor. The labels warn of the worst, but don't give great insight to the benefits.

Pancreatitis : No medication is safe. However you should consult with your endocrinologist if you are unsure about taking this medication.