Such a function is not implemented in Sponge for the same reason a /reload command is missing: It is way to much work to properly implement it in a way that is guaranteed to not leave any references and loaded objects behind. See here.
Personally I would recommend to log a long and well explained error message and than shut-down the server if you absolutely cannot continue. In my eyes, admins can be expected to dig into the server-log to find out what was wrong, stumble upon your message and either fix the error or remove your plugin.
If you go this road however, this behaviour should be well documented in the documentation of your plugin.