What are the chances that a child with selective mutism has episodes later in childhood, life?

Maybe anxiety. Selective mutism is a form of anxiety disorder. Though mutism doesn't typically occur in older children and adults, children with selective mutism are at some increased risk of other kinds of anxiety problems as they get older.
Minimal if treated. Most children with selective mutism recover as they mature. But some continue having varying types of shyness or social anxiety. See links to support groups are provided therein.