there can be backup doctors without a doctor according to the mafia wiki...
is treated as a modifier to a role, causing the role to be unusable and do nothing until another player with the same role (regardless of alignment) has died. For example, a Backup Cop could only attempt to investigate players once a Cop had died, and a Backup Ascetic could be targeted with actions until an Ascetic had died. (The role activates "upon the flip", i.e. at the end of the night or day phase in which the backed-up role dies, rather than being able to change state in the middle of night action resolution.)