Taking an array off, storing it, re-roofing and putting it back costs a meaningful fraction of the original install. So the honest advice, when we find a roof near the end of its life, is to re-roof first.
What we look for on the survey is straightforward: cupping or granule loss on asphalt shingle, soft decking underfoot, daylight in the attic, and the age on the permit record. Anything under five years of remaining life and we say so on the spot.
The good news is that the two jobs coordinate well. If you are re-roofing anyway, tell your roofer that solar is coming — mounting points can go in during the re-roof, and the flashing detail is cleaner and cheaper when it is done as one job.