Deleted App Store

Go to General settings

Scroll down to the Transfer or Reset iPhone

Tap Reset

then tap Reset Home Screen Layout and confirm

Your Home Screen should return to default layout with all build-in apps restored

You can also check parental controls settings which restrict apps from App Store:

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

Go to Settings and tap Screen Time. 

Tap Content & Privacy Restrictions. If asked, enter your passcode.

Tap iTunes & App Store Purchases.

Choose a setting and set to Don't Allow.

This is currently happening to me as well, I do follow tips on how to get it back, and it DOES work. But only for a split second or so and it just… Vanishes. This keeps repeating and I honestly don’t know what to do, I can’t get my App Store to stay visibly in my App Library or anything without it just disappearing under a few moments.

Do the instructions below also wipe your iPad deleting other apps on the iPad?

I want to reinstall the Apple Store app.

Go to General settings

Scroll down to the Transfer or Reset iPhone

Tap Reset

then tap Reset Home Screen Layout and confirm

Your Home Screen should return to default layout with all build-in apps restored

You can also check parental controls settings which restrict apps from App Store: