2002 Toyota Camry Starter gear missing

I replaced my starter in the middle of April (something was wrong with it, I don't know what). A few days ago, the engine wouldn't turn over (no engine sounds at all, but the battery seemed to be fine), so I tried tapping on the starter while my friend turned the ignition. The starter then made a whirring noise.

Took it out and discovered that the gear on the business end of the starter that engages the gear inside the engine block is missing. I'm assuming it's sitting in the bottom of my engine block, cause I don't know how it could have gotten anywhere else. So, I guess my questions are:

a) Is it gonna be feasible to try to get the gear (perhaps in pieces) out of the engine

b) If I can get it out in one piece, can I still use it (i.E, put it back on the starter)

c) If I can't get it out, would it be possible to drive my car to a repair place with another starter, or would that deal severe damage to my engine

d) If I can get the gear out, but can't reuse it, where would I get a new one (assuming I don't need an entirely new starter)

Thanks in advance for any help you can give.