“The Mishna Berura actually brings down …”
Its not so clear. The MB is commenting on the Remah who quotes the Ohr Zarua. The Ohr Zarua is discussing where there WAS a tzibbur that didnt lain. So they had a chiyuv krias haTorah that they have to make up.
It does not necessarily hold for us where there was no tzibbur that got together, thus likely no chiyuv krias Hatorah that needs to be made up