The verse says nothing about Michael holding onto Satan...The verse is discussing the future battle between Michael and Satan and his Angels...How do you arrive at your conclusion???
They are about the same event. 11Thess.2 is about the end of days. Paul tells us that Christ will not come back until after Satan.
2:3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition.
We know the son of perdition is Satan and that is who vs. 7 speaks of. He is held but will be released at the 6th trump, 6th vial and 6th seal (666 Mark of the beast) by Michael. We know it is Michael because Rev. 12:7 tells us that.
As to the identity of the one who restrains, the Church (and readers of the religion forum know that by that I mean what is commonly called the (Eastern) Orthodox Church, but which is properly the One, Holy Catholic and Apostolic Church, claims to the title ‘Catholic’ by the Latins notwithstanding) has always identified the one who restrains with the Christian Emperor, who was ‘set aside’ in 1917 with the abdication of the last Tsar.
It isn't the church as scripture tells us who restrains Satan and that is Michael.