After toggling off the generated structures during the initial creation of the world you can still use Eye of Ender which leads you to the point where the Stronghold would normally be generated. Also the command /locate for Strongholds point out that location.

How to reproduce:

1. Create New World
2. More World Options
3. Generate structures: OFF
4. Create New World
5.  Select an Eye of Ender and try to throw it

How to reproduce (/locate command):

1. Repeat the steps from 1 to 4.
2. Write /locate Stronghold
3. Teleport to the location
4. Use spectator mode and look around underground.

: