To quote myself:
These are the real problems. Not how realistic his survival was. Bringing major characters back after death is always a bad idea and never works e.g. Palpatine Reborn. Minor characters however, work. Because there is plenty of room for expansion.
They didn't find him through the force because there are ways to hide your presence, one of which was utilized by Yoda on Dagobah.
But I would consider Windu a minor char too. Certainly not minor like Maul was, but still not that major.