A: Yes, Tenable offers a 7-day free trial of Professional (unlimited IPs). After 7 days, it reverts to Essentials (16 IPs) unless you purchase.
A: Yes, but for Essentials, once an IP has been scanned at all, it counts toward the 16-IP limit (unless you reset the license – see next). nessus licence
A: Scans stop immediately. You can still view old results. You have ~30 days to renew before the scanner locks completely. A: Yes, Tenable offers a 7-day free trial