The only service we pay for as players is access to the servers. In whatever condition they are in. The Bnet account, characters, items, game data - don’t belong to us and we technically have no “rights” to it.
We can certainly be upset about a massive bug and data loss. Of course! We can certainly not play anymore and not pay to access that service anymore.
There is no part of what we pay for though that says items won’t be removed (for any reason) or that bugs can’t/won’t happen.
Yes, it SUCKS. That part is true.
The idea that you pay for them to maintain a guild bank of data, or even characters, is not true. They can turn that all off any time in all or in part. Intentionally or unintentionally.