You won't be able to go 200k miles/15 years in its current state.
I disagree, based on my understanding of how lithium ion batteries age, and are managed in EVs.
Lithium ion life is drastically longer if the batteries cycle over a narrower range, e.g. 20% to 80%, and avoid full charges and discharges. The factory "full capacity" on an EV only allows this, e.g. charges within about the 20-80% range. As real capacity reduces over time, these boundaries relax keeping the usable capacity roughly the same, but eventually accelerating battery aging. You won't see a usable reduction in capacity for a long time- probably well over 200k miles based on what I've heard from other people. This is why EV batteries last so much longer than phone or computer batteries. With the e-Golf you can also manually narrow this range further with the CarNet software, to further increase battery life.
As lithium batteries age, they do not get noticeably less efficient... they merely can't be charged with as much energy. The total range of the vehicle will eventually fall, but the cost to charge will fall proportionally.
A lithium battery using 100% capacity lasts only about 400 charge cycles, but using only 60% capacity raises this 10 fold to 4,000. 4,000 cycles at 100 miles per cycle is 400,000 miles. My e-golf is rated to 83 miles but actually gets 100-120 in my experience, unless climbing steep grades or running the AC hard.
So if EV batteries were used like cell phone batteries at full charge-discharge, they'd only last 40k miles, but I would expect around 400k life from an EV with proper software and/or an owner that carefully manages charge levels. That seems to be consistent with what high mileage modern EVs are reporting as shown in the post above (400k battery life). This would likely double again to ~800k mile life if you do only short trips in a small town and drop the full charge level via software to 75% of full capacity or so.