The Geometry mode's "Revert/Undo" tool reverses any operation on an object that has been previously modified or transformed (The creation of an object can't be "undone" - but it may simply be deleted :-).... any operation, that is, except "Delete".
An Undo-delete tool would be convenient. If the creation and modification/transformation operations and parameters of a deleted object have not been recorded, re-creating it could be frustrating, if doable at all. It is true that if one of the "File-->Save As ..." operations happened to have been used before the deletion, the deleted object's pedigree and specifications may have been preserved. Still, it would be convenient and stressless to just undo an accidental or hasty mis-step.
If that is a not easily done in the near term, then possibly a "do you really mean to delete this object" dialog might be a good alternative. Since some users (or any user from time to time) might consider this reminder to be an aggravation, it should include a "don't show me this again" check box or sub-option.
If the Undo-delete tool were added, several functional alternatives come to mind:
1) an "Undo-last-operation" (only good as an un-delete if "Delete" were the last operation done). To clarify, I am not suggesting that this function would be able to reverse-build a model from finish to start, but that it would always and only be capable of a single operation: to undo the very last operation on a geometry object. The undoing of operations previous to the immediately preceding one would not be possible.
2) an "Un-delete" that restored the last deleted object (regardless of what object it was or when it had been deleted),
3) an "Un-delete-designated-object" that restored a deleted object designated by its tag (e.g., "E3"). Since a user my not remember the tag of the deleted object, this function should probably prompt the user with a list of tags of deleted objects (from last deleted to first deleted).
Note: The parent objects that are removed when transformed, such as "B1" and "C1" in the transformation"B1+C1==>TF1", are not intended to be considered "deleted" objects in the above function descriptions.
PS A third alternative to "UnDelete"or a "Delete Warning Dialog" might be a frequent save to a temp geometry or .fea file which could be viewed at any time and reverted to if desired. The frequency and location (and name perhaps) could be configurable.