Yes, over time it will fade just like anything else in the sun for a long period of time. Usually, it will take 10-15 years to show signs of fading. Cracking of the siding can occur due to impacts on the siding or rapidly temperature changes. But we use a .044 thickness of siding.
If it is a good vinyl siding maybe 20-40 years. You will need to do some up keep on it like semi-frequent cleaning and minor repairs overtime to keep it looking good.
It depends on the age of siding. If the siding is new and the brand/style/color is still around and only a side needs to be replaced due to damage, then just the one can be replaced. But I would do a full re-side so everything is the same and you probably want a new color or style anyway to freshen up the look of your home.
The siding we use is a .044" thickness vinyl siding.
Yes, I would clean your siding semi-frequently.