Canon 1247 says:On Sundays and other holy days of obligation, the faithful are obliged to participate in the Mass.Moreover, they are to abstain from those works and affairs which hinder the worship to be rendered to God, the joy proper to the Lord’s day, or the suitable relaxation of mind and body.
Some other quotes:56. The two parts which, in a certain sense, go to make up the Mass, namely, the liturgy of the word and the eucharistic liturgy, are so closely connected with each other that they form but one single act of worship. Accordingly this sacred Synod strongly urges pastors of souls that, when instructing the faithful, they insistently teach them to take their part in the entire Mass, especially on Sundays and feasts of obligation.
[RIGHT]- Constitution on the Sacred Liturgy, Sacrosanctum Concilium
“The two parts which in a sense go to make up the Mass, namely the Liturgy of the Word and the Eucharist Liturgy, are so closely connected that they form but one single act of worship.” ** A person should not approach the table of the Bread of the Lord without having first been at the table of His Word**.
[RIGHT]Sacred Congregation for the Sacraments and Divine Worship, Instruction Concerning Worship of the Eucharistic Mystery, Inaestimabile Donum (1980)(AAS 72 p 331-346) [/RIGHT]
So the way I read it is that if you haven’t been through the Liturgy of the Word and the Liturgy of the Eucharist, you haven’t met your Sunday/Holy Day obligation. You most certainly should not present yourself to receive Holy Communion unless you have been to both, as well.
Having said that, God knows your heart. God knows if you were late for no fault of your own or if you were late due to something that you could prevent. You may try to fool yourself and rationalize being late. You may try to fool yourself and try to rationalize leaving early. You may fool others and even yourself, but you won’t fool God.
(Yes, I know that this is an academic exercise)