Why is a priest needed to consecrate the Blessed Sacrament?

[Filioque]

What if something happened and only 12 Christians would remain alive in the world. Could they never go to communion again or, would those 12 Christians make the new 12 Apostels, hence Bishops?

While from a standpoint of Faith, I don’t believe that God would allow the Episcopacy to be extinguished. One case does come to mind that had a similar tone.

In Japan after the expulsion of the missionaries, and the subsequent perescution of the Church, a group of Catholics went underground. Called by the Japanese, Kakure Kirishitan, they were only able to retain two sacraments, baptism and matrimony as they had no priests or bishops. In many areas they had no access to priests starting from around 1614 shortly thereafter the Catholic Missionaries were all expelled, until the opening of Japan with Admiral Perry’s fleet in 1848 when a Kakure Kirishitan was able to speak to the Catholic priest on board. a small group of Kirishitan wanted to see a statue of St. Mary with their own eyes, and to confirm that the priest was single and truly came from the pope in Rome. After this interview, many Kirishitan thronged toward Fr Petitjean who investigated their underground organizations and discovered that they had kept the rite of baptism and the liturgical year without European priests for nearly 250 years. Fr Petitjean’s report surprised the Christian world; Pope Pius IX called it a miracle.

So while I find it hard to see how all Apostolic lines may be severed, we do see how some were able to keep the Faith for 250 years iwhtout a pirest or bishop.

As an aside the core of the Catholic Church in Japan after 1848 were those who flocked back to the Church, There are a few who still keep their own brand of a Buddhist/Catholic underground mix of practices in some of the smaller islands off the mainland of Japan who never returned to the Church.