All my open tabs disappeared from my iPad.

Are you certain that your open tabs have disappeared - and you haven't simply opened a new Safari Window? Each Safari Window has its own self-contained set of open tabs.

When you open Safari, you may see the Shelf at the bottom of the screen - within which you will see each of your open Safari Windows; simply tap the thumbnail corresponding with the Safari Window (with associated tabs) that you wish to view.

If you closed a Safari Window - and all associated tabs - you can reopen a Recently Closed Window for a limited period of time…

Starting from a Home Screen, assuming that Safari is visible in the Dock, touch-and-hold (i.e., long touch) the Safari icon; an Action Menu will appear. 

From the menu, select Show All Windows; you will now see a screen that closely resembles the Task Switcher - but you will only see preview windows for your open Safari Windows. At top-right (or top-left for iPadOS16/17) you will see the Reopen Closed Window(s) button.

You should note that the Reopen Closed Window(s) button allows you to reopen a window for a limited period of time. If left too long, you may have lost the opportunity to recover the closed window - and with it the tabs and related tab history.

If you have accidentally closed all you your open tabs associated with a Safari Window, this User Tip may be helpful in recovering your tabs. While I have not [yet] updated the document to reflect changes in iPadOS15/16/17 (having been written for an earlier version of iPadOS), much of it is still relevant - as are the outlined strategies:

iPadOS - Safari - Lost Windows, Lost Tabs… - Apple Community

Check to see if you accidentally opened a new private tab, if so, exit private mode.

History should still have what you’re looking for. You may also have luck in reviewing the cookies stored on your device.