I thank with gratitude everyone for their contributions, thoughts and definately the amusement. (Btw, its not ~7 years~, (sic. with this many shards)... more like 7 lifetimes of bad luck!) Did my best and got four of the original cement/tar bonds off the mirror. Then the thing went "Hiroshima" on me.... and massively exploded in shards.
No damage to me, but uggggh. the mirror was toast. (Talk about a "big bang")
Any event, I'll share what I attempted and perhaps others will be more fortunate than I in their future efforts.
Removing a Large Mirror from a Cement Block Wall
Placed a 4x8 foot piece of plywood, in front of the mirror. (intended to add backing when/if I was lucky got this beast off the wall and needed to move it around a bit. It provided shielding from sharding if/when breakage occured. Then used duct tape covering said mirror, futilely attempting to prevent sharding (sic. and failed badly). Used thick safety gloves, double layers of kevlar clothing, and expensive safety goggles.
Initially re-attempted finger prying determine if the mirror bonding on the cement block wall might hopefully be brittle. No luck. Next was a simple wood saw... c. 30" length? Regarldess there was just barely enough room between the glue/tar/bonding (c. 18" from the edge of the mirror) and the block wall to allow it. I cut for 10-15 minutes very carefully, and finally seperated two of the glue/tar bonds from the mirror. The saw being covered with heaven knows what ~ghastly material~ the original glue/tar/bond truly was comprised of. Didn't handle it with my bare hands, and would not if I had I been paid to do so.... (not a prayer)
I then gently used a pry bar, followed by two very tiny shims placed between mirror & block wall, praying to get a better look at the remaining "impediments".
I attempted a third and forth bond, but was not having as much luck for some reason. I switched to simple Home Depot quarter inch, then 3/8 inch twisted wire (c. 15-18 feet in length respectively. Looked much like piano wire, only silver and the wire fibers were much bigger.) Wrapped the ends of the wire around a dowel cut into a series of 6" handles. In short, I made two really lengthy literally "wire saws".
I slipped the wire behind the closest bond and began pulling rapidly back and forth, trying to ~saw~ through the ancient globed tar. Succeeeded to cut through two more bonds in this manner. Apparently cutting at the last bond I was not pulling the wire straight enough and broke the mirror in 20,000,000 tiny shards.
However protected by the plywood sheet in front of said mirror. Nobody died...
Perhaps we can keep this thread going, in case someone else wants to try again, or alternatively succeeds!!!!