Ninety nine times out of ten, launching two humans into orbit to fix a satellite is going to cost you a lot more than just launching a replacement satellite.
The number of one-off, irreplaceable, you-have-to-fix-them-if-they-break satellites currently in orbit can be counted on one finger.
As launch costs go down, this is not going to change.
Yes it will. When costs change by orders of magnitude, trades change. Space hardware will always have some non-trivial cost, just like how equipment on the ground still has significant cost in spite of low logistics costs. As reuse lowers cost of space access by orders of magnitude, the relative cost of trashing vs fixing changes dramatically. When the space hardware costs 100x more than the launch, then it makes sense to fix than to trash.
Also, astronauts are MUCH faster at assembly than robots.
1. From the ground, you have no idea what is wrong with the satellite, whether or not the problem is fixable, and even if it is, what exact tooling/replacement parts need to be brought up.
2. Satellites are not designed to be easily taken apart.
3. Doing any kind of technical work in a spacesuit is incredibly difficult.
The extra cost of building your satellite with sufficient self-diagnostics, with a design that lets someone in a spacesuit take it apart and conduct meaningful repairs on it is going to be paid every single time you launch that satellite. This cost, in both design, and engineering is not trivial.
And the only time you'll ever get any value from it is if you go ahead and do another, even more expensive space launch - this time human-rated. This launch is likely to head on up, and discover that no, they don't have the right tools, replacement parts, or even ability to access the broken parts of the satellite.
The overwhelming cost of a satellite is the R&D that goes into designing it. If space launches are cheap, the correct economics to follow are "Just build two of them, and if the first one breaks, launch the second one."
The number of one-off, irreplaceable, you-have-to-fix-them-if-they-break satellites currently in orbit can be counted on one finger.
As launch costs go down, this is not going to change.