I know of only one documented case of the entire engine leaving the aircraft and the pilot surviving. 300-500 pounds departing will almost certainly have cg way behind aft limit.
Maybe Cub with huge elevator is exception, but a spam can with no engine is unlikely to be recoverable.
This has happened in NZ
C180 ZK-BQJ was registered to Rural Aviation 0n 1May1956 having previously been allotted the factory registration N4975A.
This aircraft joined the company's operational fleet, and was among those displayed by Rural Aviation at the Agricultural Aviation expo at Palmerston North in November 1956.
It then continued to work in the Taranaki area, and became the favorite mount of Don "Goose" Erceg. Both Don and ZK-BQJ became famous when the engine departed the airframe after propeller failure during a positioning flight on 1March1958, and Don was able recover control sufficiently to carry out a subsequent forced landing:
"In the vicinity of New Plymouth, New Zealand, in March 1958 a Cessna C-180, ZK-BQJ engaged in aerial topdressing suffered a propeller failure which threw one blade.
The resultant imbalance then threw the engine completely out of the airframe almost instantly.
As it departed the engine forced the top cowling over the windscreen, and also impacted the starboard main-wheel, cutting the tire.
The moment the engine came off the Cessna was thrown into a vertical snap roll, so rapidly that the pilot’s crash helmet was cracked when hitting the windscreen pillar!
Then followed a flat spin, from which normal spin recovery was successful.
To counter the pitch-up resulting from the rearward c of g change, the pilot applied full forward elevator, and lowered the flaps.
The ensuing flight path was controllable sufficiently to affect a successful force landing, with no further damage to the aircraft.
The free flying engine impacted in the farmer’s wood pile with no other damage to any person or property, but gave the farmer’s wife a severe fright as she hung out washing.
After a calming cup of tea, the pilot checked in with his operating company and reported that he needed a replacement aircraft, and when asked why, responded that the engine was missing.
“Have you checked the plugs?”
“No point, I can’t even find the engine!”
They took him at his word and duly arrived in a replacement aircraft, complete with engineer ready to replace plugs etc!".
Three days later after some remedial work, The 180 took off from the field and was ferried to maintenance for some rather more substantial work
