ok, depends on your comfort level with glass. If you get into the removing thing, make sure you have the rubber palm gloves and they are cleaned with acetone and shop towels prior to use. Wear long sleeves.
The silver is coming off due to the trapped moisture against the vanity top.
You can trim out with wood, or flat aluminum or xxx. Small dabs of silicone will hold with tape on while setting up.
Get exact dimensions and go to your local glass shop to have them cut you beveled strips to frame. This is one sample, there are many corner piece options. They stick on with a GOOD 3M two sided tape, as thin as you can get. Leave drainage areas. That buys you another 10 years or so.
To remove:
Use heavy braided fish line to saw back and forth (two people) to cut thru the mastic. It looks like you have no mechanical fasteners (against code btw I've had them fall off before)
Then take to glass shop to have them trim out in the strips mentioned above, cut the bad off and or cut to install in a frame of some sort.
If you do remove, when reinstalling I think the best for a 'frameless' look is nickel finish J channel. ALWAYS drill some drainage holes in the bottom strip and leave a gap to the vanity top.
Again if removing, always set at a good angle to the wall with soft something underneath, never on bare garage floor.
If you choose to re-glue to the wall, so NOT use silicone get a specifically made mirror mastic.
Cheap and to keep with changing fashion is to use vinyl tape in varying widths and colors and patterns.
Have fun.
