Sugesting petrifiy for immortality

[Tortanick]

With the new old age sytsetm you can exepct you're powerfull mages to die even if they never leave you're fortress. Since this is a major downgrade in the power of magic I'd like to recomend a solution:

A new spell for alteration allows you to petrify your mages into immortal rock. They can't do anything except keep old enchantments alive and if you lose their provience then you lose the mages and those enchantments