When you activate a beacon by sacrificing an item, the item will be returned back to your inventory after relogging.

Steps to reproduce:

1. Construct a beacon structure of any size and material.
2. Put a full stack of iron ingots into your inventory.
3. Move one of your ingots to the activation slot of the beacon.
4. Activate it.
5. Now you can see the ingot is consumed as expected. You have 63 ingots at this point.
6. Relog.
7. You'll find yourself with an active beacon and a full stack of iron ingots in your inventory.

Expected result:
Sacrificed items are permanently lost.