So the need to revert to backup programs is common in LGS-AO observing. NGS-AO backup programs with the assigned science instrument are of course easily performed. On Keck 2, we try to make NIRSPEC available on right Nasmyth during AO runs. This currently is the only focal station with a backup science instrument available on Keck 2 AO nights.
On Keck 1 the only backup science instrument readily available on AO nights is HIRES. We have not made it a habit of keeping HIRES ready during OSIRIS nights, but if you anticipate a need, please let us know.
Please note that none of the Support Astronomers (SAs) support every instrument, so your assigned SA may not be very familiar with your proposed backup instrument. If you are intending to use two different instruments for your science, it is far better to propose for both. You and your SA will then be scheduled appropriately.