1. Put your non-deletable apps in first page. Such as those default by Apple. Or don’t put any apps on first page!
2. If you MUST have a deletable app on first page, put them into folders.
3. If unfortunately the apps are already deleted, DO NOT sync and backup unto your computer’s iTunes. You can sync but please disable the syncing on your iPhone immediately! And then try and restore from your previous backup.
4. Some apps like Awesome Note, has online syncing that backs up your notes in an online account. And has auto-backing up. This, compared to the iPhone notepad is much better.
5. Build a “Recycle Bin” app for your undoing actions on your iPhone. haha.
6. Last resort: contact your third party app company to see if they can help you!