Concluding Rites
Announcements
A set of brief announcements are made at the Cathedral after the “Prayer after Communion” has been recited or chanted.  This is not a part of the actual rite, but is the place where they are inserted at the Cathedral.
Final Blessing
Next comes the final blessing which can be chanted or recited.  If it is chanted, the congregation responds with a chanted “Amen”.  If it is recited, the people acclaim, “Amen” in a loud voice.  A more solemn blessing may be observed on occasions in three parts.  Each part is followed up by an “Amen” by the congregation, either chanted or recited according to the celebrant’s lead.
Dismissal
The priest or deacon dismisses the people using one of the three options in the Roman missal.  The response by the people is “Thanks be to God”. Again, if the priest or deacon chants, the people respond with a chant.  If the priest or deacon recites, the people recite the response back.  During the Easter octave, the Double Alleluias are typically sung as a response.    
 
Sending Forth Hymn
Interestingly, the GIRM does not state that the Mass concludes with a sending forth hymn, even though that is the practice at St. Mary’s and most every parish in Wyoming and the United States.  The celebrant is encouraged to wait until the majority of the hymn is sung before processing out.  This encourages the “active participation” of the assembly. 
GIRM 90c tells us that all the ministers and all the faithful depart in peace. They “go back to doing good works, praising and blessing God,” until they gather for Eucharist again.
 
I hope this analysis of the Mass has helped to deepen an awareness of what takes place at the Mass and gives you a perspective on the importance of each liturgical action and what part music plays in the liturgy..