Is it possible for a heart to completely recover from myocarditis and congestive heart failure?

Yes it is possible: Depending on cause which is in many instances infectious or autoimmune.

Yes: Most acute myocarditis are viral and most recover within a few weeks. If the myocarditis caused heart failure and a low ejection fraction, other medication treatments (ace inhibitors, beta blockers, etc.) may be necessary to get the heart back to normal. In these cases, close follow up with a cardiologist is recommended in order to escalate therapies if things don't improve.