They believe they will not only survive it, but become the world-wide government.

The $100B in holdings are a small part of their assets. They have large real estate holdings (e.g. 2% of Florida) as well as a very diversified portfolio.

Latter Day Saints don't believe TEOTW involves the destruction of the world or even of world governments. Only the "wicked" will be destroyed at the second coming. I.e. Germany and the German government will likely still exist and operate for some amount of years after the second coming, but all wicked Germans will die off. The remaining Germans are all good people and will all eventually be converted to true Christianity (including good atheists)

Nations will slowly be absorbed into Zion, a communist utopian nation ruled by Jesus Christ himself and the world will see unprecedented prosperity for 1000 years.