There is normally no need to include any code on the logger program for always on operation. The modem is programmed to reset in the event of certain types of lock ups. However, If the power is to be controlled to the modem, then code should be included to tell the logger the modem is going offline before cutting the power off (provided by a SW12V output).
Example programs have subroutines in them to show what is required to be added to a program to do a full reset and to turn the modem on/off. It also includes examples of how to read the signal strength out of the modem and store the strength in a program variable.