From OpenStreetMap Wiki
allows to undelete objects
This plugin allows to undelete objects.
How to use
- Find out the id. of the object
- Choose "File" → "Undelete Object"
- Enter the id. and type of the object (or list of id's; e.g., n1 w2)
- Node > n123
- Way > w234
- Relation > r345
- List > n1 n2 w1 r5
- Upload the changes
The object will be undeleted preserving the old id.
What if I do not know the id.?
The current API does not allow to search for deleted objects, but it is possible to find deleted objects in various ways. See Find the id of a deleted node