If correctly removed, Widgets should not return with a restart. Are you seeing this behaviour following a simple shut-down and restart - or after a forced restart?
Force restart iPad (models with Face ID or with Touch ID in the top button)
If your iPad doesn’t have the Home button, do the following:
- Press and quickly release the volume button nearest to the top button.
- Press and quickly release the volume button farthest from the top button.
- Press and hold the top button.
- When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)
Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

If the problem persists after performing the restart, it may be necessary to reset your iPad settings. While this reset will not cause any loss of data, as a precaution, it is always wise to ensure that you have a current iCloud or iTunes backup before performing the reset:
How to back up your iPhone, iPad, and iPod touch - Apple Support
When you are happy to proceed, you can perform the reset from iPad settings:
Settings > General > Transfer or Reset iPad > Reset > Reset All Settings
If the problem still doesn’t clear, you may need to restore the iPad to factory settings - which will erase all data from your iPad:
Restore your iPhone, iPad, or iPod to factory settings - Apple Support
After performing the factory restore, you would be best advised to initially set-up “as new” with your AppleID - and test that you can persistently remove unwanted Widgets from your iPad. If all is well, you can then restore your data from your iCloud or iTunes backup:
Restore all content to iPad from a backup - Apple Support