I would only use heat as a last resort there is a chance that you could change the tensile strength of the metal or possible warp the clutch. Which clutch puller were you using the Horstman one that pulls with 5 bolts or the aftermarket puller that pulls off of the spring perches or a regular 2 or 3 jar puller? What exactly stripped? were you using air tools?
When you do get it off and you get ready to reinstall it, try installing it with no key and some valve grinding compound between the clutch and the crank. Spin the clutch by hand on the crank until both surfaces match then clean the valve grinding compound off and install the key and reinstall the clutch this will mate the two surfaces better and help it seat flush on the crank which should make it stay on and remove better as there will not be a rocking motion between the two pieces that could cause a binding or shearing on the key.