Matt Harrold ended an injury-hit season with an equaliser in stoppage time but by that point the Gulls were already looking forward to fourth tier football next season.
The visitors took the lead just after the half hour mark when Rovers' forward Tom Hitchcock pounced to loop the ball over Torquay goalkeeper Michael Poke.
Poke then saved a 46th minute penalty from Lee Brown after central defender Brian Saah fouled Hitchcock.
But on-loan Southend striker Benyon levelled when he turned in a Joe Oastler cross six minutes later.
In an end to end clash Ryan Jarvis turned the ball into his own net from Brown's free kick to put Rovers back ahead in the 55th minute.
Jarvis atoned for his error by firing Torquay level seven minutes later after Rovers keeper Steve Mildenhall palmed out Aaron Downes' header from Lee Mansell's corner.
Torquay forged ahead for the first time in the 68th minute when Jarvis latched on to a Kevin Nicholson free kick and turned the goal towards goal, where Benyon applied the finishing touch from close range.
There was to be a late twist when substitute target man then Harrold swooped to score a stoppage time leveller to give the Pirates' travelling support something to celebrate.