It should - you just need to be able to log into the RuneScape account to be able to import it onto a Jagex account. Once the account is imported, that old email you can't access has no connection to your imported account, instead it will all be through the email that is connected to your Jagex account.
Just remember it is important to maintain access to your Jagex Account email (and for now you can only import up to 10 accounts), so when Jagex Accounts are available for all to use and you set yours up be sure its an email you can always access.
29-Jan-2023 17:04:43