This rdb was rooting and 2 leaves for 1 month in a clear bottle water with aluminum foil as an outer cover to keep the light out.

Then last week, I notice the leaves were drooping.
I open it foil to see that the roots were dying, I cut out small door (with hinge) to stick my finger in to feel the dirt: slightly dry. So I add a tbs of water. Rewrap in foil, remove 1 leaf, greenhouse, place in a shady part of my house.

Today, I notice the 1 leaf left was worst off, I removed the foil to check on the status of the roots: they were worst off than before. I use my door again, the soil is moist.

See attached. What can I do to save my rdb?

-yours truly n00bs   

I was rooting several cuttings in my house and I noticed a similar situation.  A couple of them had roots that started to turn brown and it was looking bad.  About 3 weeks ago, I placed them in the greenhouse and they're now growing new white roots.  I saw you mentioned a greenhouse, but also mentioned inside your house.  Have you left them in the greenhouse during this time?  The extra humidity should spark new life in a few weeks.

yes: they have always been greenhoused but full sun. This time greenhouse in shade.  All in the house, protected from the outside environment. 

Might be not enough air for the roots. Roots perform respiration like leaves and need oxygen to do so. Perhaps cutting the bottle open and allowing some of the moisture to leave might help. 

1st i would check one inch below soil line and scratch the bark & see what happens. If good slice sides with razor for air. My guess it,will fail scratch test. If thats the case cut until good wood is found. Re root in a much lighter media. When its time to water cuttings use very little water. Doesn't take much. Just my opinion. Hope it works out for you. Will gave a,cutting for you in fall. :-)

That thing is toast. Throw it in some compost you may get lucky. Typically, once the shriveling starts it rotted at the bottom.

It doesn't look too promising from the photos but there may be a chance.
Take it out of the bottle gently, try and not damage the roots.  Check the cutting and roots for rot.  Cut out the bad parts.
If the stem and a bud or 2 are still good would then soak in water overnight to rehydrate and wash off any mold.  Let it air dry for a few minutes and then plant in a light coarse media 80% perlite.  Keep it in high humidity and see if it comes back. 

I took it out and notice most of the roots are dead. There are some alive one (short) still stuck to the bark. so I repotted it in 50% perlite and %50 compost with barks and sand. Then I place it outside under a chair (shade & no rain) with a greenhouse on top. I hope this works.

Did you scratch the bark with your finger nail.

i agree with richie and brian. its most likely rotting from underneath.

The cuttings have SIFD  "sudden infant fig death"  some varieties seem more susceptible than others. I suspect it is related to damping off in some plant seedlings.   

I would look to see if any of it is still lively. If so, I'd cut off the bad and re-root it.  It is even possible that you can root the new green growth in some coco.

what is damping off?

When I've gotten the brown roots, it's usually meant I overwatered it.  And in come the gnats...