you can extract all the XYZ values from g-code and create point cloud, or even better, parse gcode and create more points along each line... then you can use that point cloud to create mesh .. it will never be identical to original STL but it can be very close
gcodestat integrates with Simplify3D and allow you to
Calculate print time accurately (acceleration, max speed, junction deviation all taken into consideration)
Embed M117 codes into G-Code
Upload your G-Code directly to Octoprint
open source and unlicence