In "Futures End" parts one and two, Janeway leaves some 24th century technology behind for anyone to find. When she and Chakotay are in the officer of Henry Starling, she starts to download his database with her tricorder, and then leaves it behind when she and Chakotay are transported from his office. Also, when Starling steals the Doctors program he takes the Docs com badge from him. Finally, when the shuttle destroys the truck on the desert road with a 24th century weapon, that also must have left some evidence on an advanced weapon for the CHP to investgate. Resistance is futile...
I guess whether or not anything was left behind depends on whether or not the entire timeline was excised.
Our government's first response to alien or time-travel technology would be to put a platoon on it to scour the area for any evidence and remove it to Wright-Patterson AFB or Groom Lake; then to make sure anybody who saw anything was silenced and/or ridiculed. No worries!