The sweet hereafter: true or false? the snow on the morning of the accident is a symbol for the loss that would envelop the town.

I'd say this is true, because this book explores how grief is approached when a community is presented with a large-scale tragedy like the school bus accident. The area will never be the same - Sam Dent indeed becomes a different place, one many try to escape by moving away or abusing alcohol. 
So in a way, the same way snow enveloped the town, their grief and loss did.

The answer would be logical.