Will melted plug electrode always create damage?

I picked up a Pontiac 3.8 liter engine at a junkyard last week and pulled out the plugs today. The one plug has a melted electrode,the others were fine. I heard it run, seemed alright. Well today I had my wife turn the engine over with a 1/2 inch ratchet and I shown a light in the sparkplug hole,but didn't see a hole burnt in it. The heads were pretty gunky,but I am replacing them with the other heads and UIM and LIM off of her car and putting all new gaskets on it. I was wondering if I put this engine back together and see no damage to pistons or bearings from possibly getting too hot.Do you think it will hold together? By the way the engine caught fire ,but it isn't terrible looking.

The melted plug alone won't cause any damage (unless it comes off and starts banging around). But, the factors that caused the melted electrode could very easily cause damage; detonation, wrong heat range plug, improper timing, etc.

I would say that if you pull the head and don't see any cause for the electrode melting, (excessive carbon buildup, evidence of blowby, leaking head gasket) I would go ahead and reassemble. Make sure the plugs are the right heat range and see if it happens again?