Are you using your Yahoo email address to identify your AppleID account - i.e., is used to sign-in to iCloud and Apple services? If so, be careful to update your AppleID account to use a maintained account (such as your new Gmail account) with which you can continue to receive email.
In the event of needing to recover access to your AppleID account, your primary email address is used to receive critical reset instructions. If you continue to use an old/unmaintained email address to identify your AppleID account, unless you can access the associated email account, you may be permanently locked-out from your AppleID.
AppleID
An AppleID account is intended to be used for life. If you need to change the primary email address that identifies your account, a secondary (recovery) email address or trusted telephone numbers, you need to update your AppleID account as necessary.
Change your Apple ID - Apple Support
Change your Apple ID password - Apple Support
What to do after you change your Apple ID or password - Apple Support
Change, add, or remove Apple ID payment methods - Apple Support
Few of us will have the luxury of forever keeping the same email addresses or telephone numbers - sometimes these needing to be changed for a variety of reasons. However, updating our AppleID account, maintaining access to our data and purchases, is easy and relatively straightforward - accommodating life’s many changes as they occur. Using a completely different in place of maintaining your existing AppleID account can introduce many complications and issues, not limited to losing access to paid Apps, subscriptions and services - these being forever tied to the AppleID account from which they were purchased.
Mail
If you have a new email account, you'll likely want to use the new account with your iPad's Mail App. To do so, you simply need to add the new account to your iPad settings:
Add an email account - Apple Support
Deleting your old email account from your iPad might be unwise - at least in the short term. It is perhaps inevitable that someone from whom you need to receive email - in particular for other accounts and services that use the email address to send reset or other administrative mail - will be forgotten. Maintaining access to an old email address mitigates a situation where a critical email is sent to the old account.