Several months to years, but not forever.
We (obviously) don't yet have astronaut footprints to examine, but we do have rover tracks to look at.
Here is a perfect example: Opportunity's tracks around Victoria crater.
As we can clearly see, over the span of one Martian year the tracks have faded a lot, but are still crystal clear.
Similarly, here is a close-...
As Sujay says, Mars is known for it's dust storms, therefore footprints wouldn't last long on the surface. The regional Martian dust storms tend to happen in the summers and the larger, planet wide, storms every few years.
However, while I cannot find anything categorically stating the dust storms don't reach the top of Olympus Mons. The vastly lower ...
Answering my own question: Juno is going to search for plumes, but rather than using UVS, it will use JunoCam and Stellar Reference Unit cameras. It is going to perform a close flyby, 320 km, 29 September 2022.
Ingenuity is a low cost technology demonstrator. As a technology demonstrator, NASA and JPL cut lots of corners to keep the cost low (low by NASA standards, only \$80 million US compared to the \$2.2 billion cost for the rover). Ingenuity was planned to make just five flights during the first few months of the mission. If it had fallen short of this goal of ...
The answer is easy, it was given in your link to the NASA website:
When we designed and tested Ingenuity on Earth, we expected
Ingenuity’s five-flight mission to be completed within the first few
months after Perseverance’s landing in February 2021. We therefore
prepared for flights at atmospheric densities between 0.0145 and
0.0185 kg/m3, which is ...