I think Transdniestria is about evenly divided between Romanian-speakers, Ukrainian-speakers, and Russian-speakers. It will probably remain under Russian control regardless of whether Putin annexes the rest of Ukraine...just like the Kaliningrad area belongs to Russia despite not being adjacent to the rest of Russia.
The thing is that while Transdniestra is wholly dependent on Russia (and formerly Ukraine), it was never taken over by Russia. But if all these oblasts were to separate from Ukraine (which I highly doubt), I’m sure Transdniestra would unify or all-but-unify with whatever republic novorussia forms, or if Novorussia joins Russia, it would join too... and be contiguous.