I've had gastritis due to stress and acid reflux for about 5 months now... for me, it keeps getting better and coming back.
So yes, Gastritis can unfortunately recur, especially without a change in diet/lifestyle. It's caused by stress
, coffee, alcohol and sometimes by a bacteria called H. Pylori.
You might want to get tested for H. Pylori to see if you have it, eradication of H.Pylori will lower your chances for recurrence/complications.
Yes, Gastritis can lead to an ulcer if untreated for long enough. About 1 in 10 people end up with an ulcer of some type at some point in their life. People go many many years dealing with uncomplicated gastritis/ulcers, don't be worried about the big "C".