Unless your working draft was saved to the Drafts folder, there is no method by which to recover the [now deleted] email from your iPad.
As originally outlined, Continuity transferred the email from your Mac to to your iPad - as it was designed (and configured in your Mac/iPad settings) to do so. With the Mail App be immediately terminated on the iPad, prior to be accessed on the iPad, there would have been no opportunity for the iPad to have saved the draft.
Unless an iPad App has frozen or is malfunctioning, there is no benefit benefit in terminating (i.e., force-closing) an App. iPad resource and memory management is designed to minimise the system resources used by an App unless it is a foreground/running process. Terminating and relaunching an App is considerably more resource intensive - and consumes more power - than allowing system resource management to it job.
As such, you son accessing your iPad and immediately force-closing the Mail App, was ultimately the reason that you lost your draft email. As unpalatable to accept as this may be, this was as the fault of the User - not the System.
iOS/iPadOS Apps consume very little (if any) system resources and/or power when idle. Apps are generally in one of four states:
- The App is “Active” - it is running running in the foreground. When you switch tasks, the App will continue to run in active state for some minutes before its resources are released and is placed into an Inactive state.
- The App is “Inactive” but remains loaded in [fast] RAM. In this state, the App can be instantly restored to an Active state - but is not consuming CPU or other resources whilst in the inactive state.
- The App is “Inactive” and unloaded. In this state, the App has been completely offloaded (releasing RAM for use by other processes) but its running state has been saved to [slow] flash memory. Returning to an App in this state will cause the App’s saved state to be reloaded from flash memory into Active RAM - without the need to re-initialise the App.
- The App has been closed. All running data has been expelled - there is no “saved” state; relaunch will reload and re-initialise the App from scratch.
iPad Resource Management is very efficient if allowed to operate as intended. Continuity, when enabled, is designed to allow instantaneous and transparent task transfer between multiple devices by a single User; Continuity cannot accommodate simultaneous use of a single-user device (i.e., your iPad) by multiple Users.
If you wish to share your iPad with other Users, so as to avoid the very situation in which you find yourself, you must disable Continuity functions. Also consider that all your personal/sensitive information is exposed when sharing single-user devices - such as iPad and iPhone.
There you have it - cause and effect.
I’m sorry that you’ve had to learn about Continuity functionality in the manner that you have, this evidently leading to loss of a draft email. Perhaps take solace from this unfortunate learning-exercise in that you might have lost far more than a single draft email.
Should you wish to revisit Continuity and its settings, here again is the direct link:
Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support
I sincerely advise that your seriously reconsider sharing of your iPad with other Users, regardless of your Continuity settings. Sooner or later you will likely experience significantly more than minor data loss - such as compromising your sensitive or financial data, loss or deletion of passwords, account lockout, or perhaps total loss of data.