Like casey, it never lasts very long in my fridge. But this is my take on sausages and yes, I know it is certainly NOT very scientific - but works for me.
To me: Summer sausage is a soft, very pliable cured meat. The softer the higher the moisture content, the higher the moisture content the faster it can spoil. Usually on the larger side in circumference. Bologna types.
Drier, harder sausage has less water content, ergo lasts longer. Smaller circumference, much more compact and harder. Think pepperoni type.
As I said, not scientific but seems to work for me.
So use up the softer ones - I would say within a week and the harder ones, depending on how well you rewrap them much longer. Except in my place as I will have eaten it all up before you can make a 2nd meal out of it.