Hm.. I think getting low on mana mainly comes when nothing makes you spend addersgall (like in situations where Kardia is enough and no need for extra heals).
Sage doesn't have a stack-dump like scholar has energy drain. May be worth (though feel bad) to throw out a addersgall spender (probably the one without CD) even when no healing is required, simply for the mana restore and to keep the charge CD going for continuous mana restores.