More than likely, it is the switch. It is not sealed, so dust and debris will eventually gum up the contacts in the switch. I have many times taken the switch apart, and cleaned the contacts. It has always been the issue.
I teach scroll saw at the local Woodcraft store and have had a saw quit working in mid class. I can take the switch apart and working in about ten minitues.
To remove the switch, first unplug the power cord, then remove the 4 torx screws holding the control housing to the saw. With long nose plyers, pull the two wires off the switch. Pull from the wire conectors.You also have to disconnect the conector coming from the speed controller. Once you have the housing removed look inside. You will see two clips holding the switch in place. Use a screw driver or your fingers to squeeze the clips towards the switch, then push the switch out! To replace, reverse the process.
Good luck!