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.