If you don't want to open everything right away, put protocol specifications, keys and the like into escrow somehow, to be published when the service is discont

If you don't want to open everything right away, put protocol specifications, keys and the like into escrow somehow, to be published when the service is discontinued (it can't be tied to the company or brand because there will always be some form of legal successor). Run a domain called $productname-support-beyond-the-grave.com or so where the escrowed data would appear and for the time being use it to explain what you are doing and why buyers should be wary of competitors without a similar commitment. Keeping a repository like that up to date costs a lot of money, the shameless self-praise is how you would make it agreeable with budgeting. There should be a service for that, with people who can build experience over multiple client lifecycles and a recognizable brand, maybe even a 3/4/5 star commitment rating that would go down e.g. when there are indications that the repository is getting stale relative to the deployed service/firmware of the still living company.