The motor sprocket is very likely to be worn, and a new chain won't run well on the old one. It's definitely worth replacing all three, chainwheel, motor sprocket, hub gear sprocket, as well as the chain to get them to run well together.
Your frame should last practically for ever, the question mark is always the motor unit. Some of them have run ever since first introduced in 2001, while others have developed the odd unrepairable fault after a few years, it really is a matter of luck.
I think the best bet is to replace the chain and sprockets which is not too expensive and just carry on in the hope that you'll get enough further life to justify that moderate expenditure. Then if you do get a more serious failure it could be time to start afresh with one of the later bikes and enjoy the added features like the high power mode and longer range.
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