Parts will be avaliable as long as GM is in business. As for resale, the market detemines the value. The unfortunate thing for Pontiac (and all of GM for that matter) is that until recently, their cars did not hold up well over time so resale values are much lower than comparable Japanese cars. Now, Pontiac has the additional problem that their line is being discontinued. This gives the perception that they're 'going out of business', and even though this isn't true, it does affect the market value (what people are willing to pay) of used Pontiacs.
The good news is that pretty much all 2008 Pontiacs are of good build quailty, and even though the resale value might not be high, you should get a reasonably good deal upfront.
