Apart from this option, CEUR-WS has been online since more then 20 years and still publishes old volumes from 1994. Paper-based proceedings of many workshops from that time are virtually unavailable these days.
So, what can make a volume disappear from CEUR-WS.org?
First, the copyright issues may have been neglected by you, i.e. you did not acquire appropriate rights from the authors. If we become aware of such a situation, we may remove the complete volume to limit the damage caused by the negligence. So, please take care that your authors explicitely pass the copyright for their papers to you.
Second, we may become aware of ethical issues, such as plagiarism. Plagiating papers must be removed. If you become aware of such cases, you should discuss with us the right way to implement the removal. If we become aware of plagiarism and you are not reachable to discuss the issue with us, then we may remove your whole volume to reduce the damage.
Third, we may be running out of technical and/or human resources. This is not likely any time soon but there is also no guarantee that we always shall have the necessary resources. CEUR-WS.org is free to you, but it is not free of costs for us and our organizations.
Fourth, there could be a technical breakdown (e.g. disk crash) or a human fault on our side. We try our best to avoid it but it can always happen. You are strongly advised to keep a copy of the published volume, so that it can be recovered even when our own backup procedures fail.
The fact the a volume disappears from CEUR-WS.org is not an unusual event. It can be compared with hardcopy books being out of print. Long-time archival is not a service of CEUR-WS.org but rather a service of (national) libraries.
The word "you" refers to a proceedings editor submitting a volume to CEUR-WS.org. The word "we" refers to the management of CEUR-WS.org.