If for any reason, accidentally or intentionally, some content from a page got deleted, there are a few ways in which you can get it back.
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​Using WordPress with 3rd party themes:The WordPress revisions system stores a record of each saved draft or published update. The revision system allows you to see what changes were made in each revision by dragging a slider (or using the Next/Previous buttons). The display indicates what has changed in each revision - what was added, what remained unchanged, and what was removed. Lines added or removed are highlighted, and individual character changes get additional highlighting. Click the 'Restore This Revision' button to restore a revision.

The revisions page also includes a 'compare any two revisions' mode that allows you to compare any two individual revisions. In this mode, the slider has two handles, one representing the revision you are comparing from and one representing the revision you are comparing to. Drag the handles to see what has changed between any two specific revisions. Note: the 'Restore This Revision' button always restores the revision you are comparing to.

To return to the post edit screen without restoring a revision, click on the post title at the top of the page.
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To access the Revisions, edit the post/page in the backend and click on Revisions:

Using the Divi/Extra theme or a 3rd party theme with The Divi Builder plugin:

In addition to the Revisions, when you use the Divi theme, which has the Divi Builder already included when you install it, the builder has an option of Undo the changes. So let's say you are building a post/page and by mistake you deleted a section/row/module, you simply go to the builder and click Undo.
​Backend builder:

Visual Builder:

Hosting backup: 

If for any reason, the above methods don't work, try by contacting the hosting company which hosts the website, almost any company stores a backup on the server going back 30 days. 

So contacting them to restore your website to an earlier date will help you get your content back.

Wayback Machine:

If the content you want to restore goes back more than 30 days, you can try your chance with the Wayback Machine website.

They hosts more than 338 billion web pages saved over time and they can help. 

Visit https://archive.org/web/ and insert your website in there: 

If your website has been indexed by it (good ranked ones are automatically saved) there is a good chance to see your old content going back months or even years ago.

Just click on a date in the calendar and see your website: 

For example, I can retrieve a whole post from https://elegantthemes.com from 2012: 

Note:It's always recommended after big changes brought to a website, to do a proper backup.