Main reason it wouldn't work is that once a bit is lost in the bottom of the hole, that portion of hole is done, el fin. These bits are diamond impregnated PDC bits and you cannot drill or mill through them. Once you've dropped one, it would be a required side track.

Now you might ask, cool so just drill around it.

The problem is that with current technology, you HAVE to pull back to the surface first in order to do this. You need to cement the bottom of the current hole and depending on the circumstances, you also need to set a 'whipstock' in order to assist in drilling out of the original hole. Side tracking is a long and arduous process that involves numerous trips out of the hole.

So regarding your lower comment, that's why we can't just have multiple bits and drill around them, or drop them off in their own sidetrack. It's not a bad idea, it's just that the realities of drilling at these depths are harsh and not completely intuitive.

My Creds - currently in the gulf of mexico drilling a well with a total depth of 30,012 feet.