Note that this isn't guaranteed, especially for smaller bands that get picked up by a label. Most of the time the label just makes the releases hidden, so they're no longer displayed publicly, but can still be downloaded. However, some labels delete the release instead, so it's no longer downloadable from your collection.
The best approach is to take advantage of the fact that Bandcamp lets you download everything and simply download everything you buy and keep backups (as you would with any other important data)
Even if there aren't labels requiring artists to hide or delete music from Bandcamp, you never know if Bandcamp could just go down one day for financial reasons and then you're screwed.
Beets doesn't maange handle the extra files that the zip often includes, such as PDFs of linear notes, the sheet music I once found included, or band photos. Maybe someday I'll figure out a good archive for everything that isn't "the literal zip file".
Oh, wait. They did already!
https://www.federalreserve.gov/paymentsystems/fednow_about.h...
Bank transfer isn’t universally the most popular method of e-commerce transactions. For example, PayPal seems to be the most overwhelmingly popular online payment method in Germany. In the UK, PayPal and debit cards are the leaders. Debit cards are also generally popular globally (a debit card isn’t the same as a bank transfer).
https://blog.2checkout.com/popular-online-payment-methods-gl...
https://www.rapyd.net/blog/the-top-payment-methods-in-the-un...
This speaks more toward someone like a musician needing a solution that has many payment options to appeal to a wide breadth of customers, not some kind of dig on US e-commerce and banking because “Europe does it better and the US is stuck in the 19th century.”
That "on your server" part is going to make is unsuited for 99.9+% of bandcamp artists, and speaking as someone who buys an awful lot of music on bandcamp, I would have some concerns as well. (Not least of which being that with bandcamp I can download purchased music years after purchase, even if artists have died or bands broken up, I wouldn't have that guarantee here).