28 Years, that's the time Equestria's technology rise took and until they finally got to the point at where they could bring Rainbow Dash back, and when she finally was back she wasn't afraid anything that went into the direction of death. Why? Join her husband her son and his friends when she tells them.

"Once you saw and beaten death, you don't care about anything." Is her simplest answer

In this Season Rainbow explains how she survived while she was heavily wounded and in a coma.