While Anker puts it a bit strong I'm with him.
The issue of the system losing coolant is minor compared to the issue of the system unable to hold pressure when the coolant is hot.
It is the pressure that keeps the coolant from boiling once it reaches 212F. (If the radiator fans come on on their own the coolant is at 212F.) This lack of pressure control can allow steam pockets to form in the hottest areas of the cooling system which is in the heads around the exhaust ports/valves. If a steam pocket forms this can block coolant flow and the area becomes superheated, that is heated way more than it would be otherwise.
I think it important to note that while head gasket leaks with these engines are *rare* (rare in I can't recall ever coming across a report of a head gasket leak) cracked heads are not rare. While not common place thankgoodness cracked heads happen far more often than is comfortable.
You will not save enough money from postponing the coolant tank replacement to cover the cost of addressing a cracked head.