Jesus didn't instruct his Apostles to make disciples in Matt 28:16-20. He commanded his disciples to make disciples. So if we are not making disciples, are we disciples?
"Now the eleven disciples went to Galilee, to the mountain to which Jesus had directed them.17 And when they saw him they worshiped him, but some doubted.18 And Jesus came and said to them, “All authority in heaven and on earth has been given to me.19 Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,20 teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age.” Matt 28:16-28
And just because it is not written in the epistles, it doesn't mean that people weren't evangelizing a lost world. The epistles were mostly written for correction, and private teaching to Timothy and Titus. They were correcting doctrinal error. So if the people were active in making disciples, which they obviously were, since the gospel spread like wild fire throughout the known world, then there would be no need to rebuke them for not doing it.
I truly believe that we do need to be witnessing to people. For most people, friendship evangelism is the most effective these days. So that means hanging out with the lost, instead of our Christian friends and family, and praying for those lost people. God will open doors if we make ourselves available.
As for the apostles overriding the last command of Jesus, found in both Matt 28:18-20 and Acts 1:8. It was the last command of Jesus before he was taken up to heaven. Also, read the book of Acts. It really is the story of the birth of the church, and how the gospel spread. That explosion of the gospel wasn't limited to 11 (or 12 including Paul) disciples or apostles in Acts. People were all working towards the common goal of making Christ known.
So beware of complacency, indifference and rationalizing away this command of Jesus! And no, I don't think we are to stress out over this, but pray for God to open doors to witness to the lost we meet and know.