I'd recommend getting the one to the vet, and setting up a new enclosure for the lost one, once you find it.

You should never house ball pythons together - they don't desire each other's company, and "cuddling" behavior is actually dominance. Dominance causes stress, which can lead to illnesses like RI's.

Additionally, new animals should be quarantined in a different room from your existing animals for 60-90 days, and always handled last.

Good luck with both of them.