It varies but in general a certificate authority's root certificate is good for about 5 years. As long as our server certificate uses the same certificate authority, we should generally have up to 5 years of version checking without all users needing to update VaultWiki to get an updated bundle, regardless whether we renew our server certificate every year.
The one for the company we use was set to expire in 2020. However, it seems like that certificate authority changed their company name last year, so when our server certificate renewed this year, the authority's name did not match any more. The authority's certificate, which will be rebundled with VaultWiki, still expires in 2020.
This means that we should have the same problem again next year. But after that I would expect it to last about 5 years unless they change their name again.
A link to check manually on a connection failure is a good idea.