We actually do have a few cases of documented impact sites of artificial probes on Moon, Mars, and Earth:
Moon
On the moon there is no atmosphere to slow an impacting spacecraft down, so the spacecraft, if not at least attempting to break will be traveling with the moon's minimal orbital velocity of $1.68\,\frac{km}{s}$. There have been a few intentional impactors, but two in relatively recent times that have been imaged from orbit. Both from LRO:
(Image Credit: NASA/Goddard/Arizona State University via WikiMedia commons)
(Image Credit: P Stooke/B Foing et al 2017/ NASA/GSFC/Arizona State University via Europlanet Media Centre at phys.org). About $50m$ wide.
The first image is of the impact of the LADEE probe, which was about $2\,m$ long, the second and third are of the SMART-1 probe, about $1\,m$ long.
Both images show clear ejecta streaks and impact crators, but not a whole lot of debris. Both had an impact velocity of around $1.8\frac{km}{s}$. Not much of the spacecraft seems to be left. Traces of metal and other artificial materials can probably be found, but not a whole lot of recognizable structure. But it is hard to make out the details from that altitude.
Mars
There have been multiple kinds of impacts of probes on Mars that we have imaged:
(Image Credit: NASA/JPL-Caltech/MSSS via WikiMedia commons)
(Image Credit: NASA/JPL-Caltech/Univ. of Arizona via WikiMedia commons
ESA's Schiaparelli EDM lander performed a nominal entry into the Martian atmosphere, but due to a sensor malfunction jettisoned its parachute too high, firing the thrusters for too short and dropped onto the surface from $3.7km$. It crashed with about $0.15\frac{km}{s}$, also being around $2m$ in size. The heat shield (top right) and parachute (lower left) appear to have reached the ground nearly intact (they behave a bit more like a piece of paper: big surface area, but little thickness, thus dropping slower), but the lander (top left) has been spread across the landscape. It also shows clear ejecta streaks and a crater of approximately the size of the craft. In this picture however there might be some spacecraft fragments that are visible (the light spots around the image). They might be just image noise, but it is likely that some pieces survived the impact.
(Image Credit: NASA/JPL/Malin Space Science Systems via WikiMedia commons)
(Image Credit: NASA/JPL via WikiMedia commons)
Opportunity had the unique opportunity (get it) to actually image its heatshield that had impacted Mars after separation. It's impact is probably comparable to that of Schiaparelli's components. Both should have reached their respective terminal velocities upon impact. In the picture you can see that the impact crater is quite shallow and that the heat shield is mostly intact (or in big pieces). It however did not contain any fuel.
This is probably similar to what happens to most artificial objects entering Mars: if they survive the entry they impact with something close to terminal velocity.
Earth
(Image Credit: John Hayman via WikiMedia commons)
Some first stages of rockets (that up until now never reached orbit) have come back down to Earth rather intact. In the image is Britain's Black Arrow launch vehicle. This specific one crashed onto the ground. The Saturn V's F1 Engines actually hit the water in such a way that the could be recovered.
(Image Credit: Rycho626 via WikiMedia commons)
(Image Credit: NASA)
Pieces of the Skylab Space Station survived reentry in such a way that big pieces could be recovered and be recognizable. Some tanks from rocket second stages also made it.
However most satellites and stages entering Earth's atmosphere don't make it to the ground and end up as dust raining to the ground
Conclusion
- If their is no atmosphere: Craters with ejecta
- If there is some atmosphere and you survive: Craters with ejecta and some pieces of all sizes close together
- If there is a lot of atmosphere and you survive: Some single pieces. But usually you don't survive
