At 100% stability, SAP's will close with valuable rewards:
Active hacking: level 9/10 decoders, 5 - 6 cortexes, 2 x beacons
Destroy: Syndicate-exclusive ammo, 2 x beacons
Passive hacking: 0.5 mil Epriton, 2 x beacons
Specimen processing: Epriton isotopes, 2x beacons
Note: completing a SAP for an outpost your corporation own also results in stability going down. Wait for it to close (after 1 hour).