Just an idea to stop people from staying graced like forever without costing them much at all except one death.

For simplicity's sake, let divine grace melt away every new year's day.

Either that or base the maximum length of divine grace on your level. For example a newbie of level 1 can stay graced for 80 Achaean days, while an old geezer at level 80 can enjoy it only for an Achaean day.

As for people killing newbies constantly for easy experience, just make it a default that newbies will remain in divine grace until level 5 or 10, not being able to reject grace even.

Mistral

Penned by my hand on the 12th of Miraman, in the year 261 AF.