If you light a match, possibly. (JK. But seriously, chronic gas & bloating may be a sign of other issues. From minor food allergies to more serious digestive/bowel issues. Your doctor should have offered advice when he diagnosed it, yes?)
No. My brother has it. He had H1N1 when it came around, which attacked his digestive system. He went almost 3 years undiagnosed, missing 2 years of high school. Now he's been diagnosed with IBS and is finally back in school like a normal kid again, finishing up his senior year. With Gastritis and IBS, you need to watch what you eat and how different foods affect you. Talk with your doctor about taking a probiotic also. Everyone should really be taking a probiotic, whether it's from eating foods with probiotics (such as yogurt) or taking a pill. Any other questions, just ask me. :)
While death is possible, it would be unlikely but that doesn't mean the condition isn't serious. Left untreated, gastritis may lead to stomach ulcers and stomach bleeding. Some forms of chronic gastritis may increase your risk of stomach cancer.