Remove Linear Good From Quasi-linear Utility Function
This is one possible interpretation. Good 2 being removed from the market can simply be interpreted as $x_2 = 0$. In an economic interpretation the good does not simply disappear from the utility function in the sense that preferences do not change, it is just the availability of the good that changes. This is an external condition, so you can simply think of this as a market constraint $x_2 = 0$. 

Now, looking at indifference curves as the different bundles for which the consumer obtains the same level of utility, and defining this level as $k$. It is clear that for any $k$ when there is only one good, each "indifference curve" will consist of only one point (in particular $x_{1}|u(x_1,0) = k$). In a 2-D graph this will simply correspond some point ($x_1$,0) for each $k$ level. 

The demand function should be quite straightforward.