It's possible, but difficult, as the plant has no water-uptake mechanisms, but can still lose it through normal transpiration.
If the spike is dying, the water supply to the keiki will fail as well.
If this is a "special plant" and you're willing to go to extremes to save it, I'd remove the keiki from the spike and do the following:
- soak the keiki in a good stimulant product.
- briefly dip it in a 1% bleach solution to remove any pathogens on the surface
- nestle it into loose, moist sphagnum in a sealed container, kept warm and shady.
That'll give you a saturated air environment to slow desiccation with a reduced fear of rot - the sphagnum should be self-protective of that.
Then hope and pray it can grow roots before it desiccated to death.