i) is there the possibilety to copy the current "image"
Yes, of course. The machine can read the flash rom, after all (how else would it boot?)
ii) if the flash failes is there any way to get the machine running again
As long as you don't overwrite the tiny reflash thingy that's there on most BIOSes; yes. Do keep an emergency floppy at hand, that you verified to work, though.
iii) how much time will this take me?
If you know how to write to flash memory, and have the specs that tell you where the write protect is; not more than 30 minutes or so. If not --> much much longer.