deathbed conversion

Short definition from Wiktionary

Noun

1. 1
   Acceptance of religious belief immediately before one dies, typically in a state of anxiety or fear of the insecurity of what will happen to one in and after death.
2. 2
   An abrupt, last-minute change in one's professed beliefs, principles, or point of view in order to escape a serious threat or to increase one's chances of success.