Brake pads eventually need to be replaced, but they should last a long time due to the use of regenerative braking. The main "consumable" cost of operating the car should be tires.
The battery pack is rated for 100,000 miles. In fact Tesla estimated it should last 125,000 but decided to be cautious and officially call it 100,000. At that point the capacity has degraded to 80% -- you could continue driving it if you can live with the reduced range and power. It does seem likely that the battery technology should be improved by that time, so you'll have more incentive to replace it.
The electric motor has ceramic bearings that are rated for 100,000 miles. I assume it should be possible to get those bearings replaced instead of having to replace the whole motor.
The biggest mechanical worry I have is the transmission. It looks like it's unique -- who designed it, where did it come from? Will it be durable over the long run and survive all the stresses that high-torque motor puts on it? I had a little qualm when I was reading the recent "test drive" report in Popular Mechanics, they said the car was locked in 2nd gear because it was an engineering prototype and wasn't ready to withstand being shifted! Let's hope they get that sorted properly, eh?
After 100K miles you go into longer-term thinking, and your main concern would be things like. . . wear and tear on the steering and suspension. . . wear and tear on cabin switches and upholstry. . . gas struts need refurbishing at some point. . . And stone chips in the paint job, don't forget! (It hasn't been mentioned, but the car really should come with some protective film like Lotus's "Star Shield", which is optional on the Elise. Practically everyone who got an Elise without Star Shield soon wish they had it.)
The fascinating thing about all this from my standpoint is, we're talking about an exotic sports car here -- and the maintenance costs on exotic sports cars are usually murder. I've already had this experience with my Lotus Esprit V8, which falls in exactly the same price category as the Tesla Roadster. "You're charging me how much for an oil change?" Squinting at the service bill. . . "Are these some new kind of spark plugs made from gold?" I've heard Ferrari owners have it much worse, even.
If you plan to keep the car a long time and drive it a lot (and who wouldn't?), and if we assume gasoline prices only go up from here (as seems all too likely), you could easily save $30,000 and a lot of hassles over the life span of the car compared with conventional high-performance sports car. It makes the Roadster actually look like a bargain next to most of them.