The new roots are not likely to hydrate the old pseudobulb much, if at all. But they'll take care of the new one. The plant eventually will suck the old p-bulb dry (but that why the plant keeps them - they're the reserve that keeps it going while it is working on growing the next set of roots and pseudobulb.)
Once they’re happy, these guys will produce roots like crazy. Most of mine have required repotting after a year. I’m trying a lot of them in clay to limit exploding pots.