Show-Me the Argument

In Chapter 6 Lycan talks about ‘Use’ Theories such as the Wittgensteinian view.  According to these views language does not bear the expressing relation to propositions, instead language is an activity similar to a game.  So, as Lycan says according to these theories “a linguistic expression’s meaning is constituted by the tacit rules governing its correct conversational use” (pg. 91).  Here’s my worry—if meaning is determined conventionally according to the rules of the language game, what implications does this have for our conceptions of necessity and possibility?  It seems to me that if the meaning of a sentence that we normally think expresses a necessary truth only has that meaning through convention and it is not expressing a proposition that is a necessary truth, then that sentence does not express a necessary truth because the rules of the language game, which are established by convention, could be different.  So, how are expressions that contain modal concepts understood given a ‘use’ theory?

Kripke has an example (pg. 45 Lycan book) where a man named Schmidt is the one who actually proved the Incompleteness Theorem and Kurt Gödel merely discovered Schmidt’s manuscript and published it under his own name.  Most people only know Gödel as the man who proved the Incompleteness Theorem, yet when these people utter “Gödel” they are referring to Gödel, not Schmidt.  Would this way of referring occur in the following example: 

Assume the same information from Kripke’s example. Bob knows Schmidt by sight and he knows that Schmidt is really the one who proved the Incompleteness Theorem.  Joe doesn’t know anything about Schmidt, he knows Gödel as the man who proved the Incompleteness Theorem, but doesn’t know Gödel by sight.  Jim doesn’t know anything about Schmidt or Gödel.  Bob, Joe, Jim, and Schmidt are all at a party, Gödel is not there.  Bob sees Schmidt and points him out to Joe by telling him “that man is the one who proved the Incompleteness Theorem.”  Joe later bumps into Jim at this party and tells Jim “Kurt Gödel is at this party”.  In this case, is Joe actually referring to Gödel by uttering “Kurt Gödel” or is he referring to the man that proved the Incompleteness Theorem, who Bob pointed out to him?  If Joe is actually referring to Schmidt, what is the difference between this case and Kripke’s?  Thoughts?