Catholics are accustomed to pray for a happy death - rather, they ought to be. What is happy about death? It is dying in the state of grace, dying in the Lord.
Today's gospel, the prophecy of Simeon captures it well.
"Lord, now let your servant go in peace;
your word has been fulfilled:
my own eyes have seen the salvation
which you prepared in the sight of your people,
a light to reveal you to the nations
and the glory of your people Israel." - Luke 2