At the End There Was You (Blue Fairytales, #1) by Wendy Heiss

The world will end in seven days.

Winter is a Priestess, her life is simple and uncomplicated, but shortly takes a turn when she is appointed as an aide for a Mage who intends to stop the God of Death from spreading a plague that would end their world. Both of them begin searching the Urvalis library for answers and find more than they had bargained for.

And as the end approaches, the questions begin vaguing.