How long do you guys warranty your work?
Ten years because that was standard in the solar industry here to get early govt incentives (now gone). I realize that is unusually long. The 1 year Rick mentions is much more common.
How long are we responsible for our work?
Liability wise? Basically forever on your workmanship, unless someone else messes with it or it gets damaged by accident or other such things. You are less responsible for the longevity of the products you install, that is mostly on the manufacturer. If you can point to defective product instead of your workmanship you may have less liabilty.
Keep your insurance coverage active!
Meaning, there have been times when I have returned to a job where someone else has performed work and had disrupted my prior installation (Example Generator Install at a home). ..
Then you are not responsible for it anymore, especially that portion they disrupted. You can blame them for anything that goes wrong, and it would be prudent to do so or at least refuse to accept the blame yourself. If it were brought to a court of law over some incident I bet your lawyer would probably tell you that the best strategy is to blame whoever disrupted the installation and/or cast doubt upon how responsibilty can be determined.