In an attempt to speed process of defrosting freezer, I unplugged unit and began to heat accumulated ice with a heat gun, did not notice until to late that I melted a portion of the side wall, is this danderous, will the refrigerator stop working, will all the freon escape, possible overheat danger or food contamination. Can it be repaired with some sort of adhesive glue/filler.?
Is it time to buy a new refrigerator?

Not usually dangerous, most likely will not lose freon, not a health issue unless food can get trapped behing the wall. Use metal duct sealing tape, won't look great but who else looks in your freezer. Of course you couls help the economy and buy a new one but I would just let it die a natural death.

Why did you need to defrost the freezer? Most are self-defrosting unless you have an older model. I doubt melting a small part of the plastic will cause a problem. Just seal it up and it should be okay. DrTom4444