How long do you imagine it takes a starter to change from commercial instant yeast to wild yeasts?

I have a starter that I made from half-teff, half-AP flour and instant yeast about 2 months ago. I fed it for just a few days before storing it in the fridge. I kept it just because I didn't need all of it for the injera I was making. I stopped feeding it teff and started feeding it half whole-wheat and half-AP flour.  I feed it about once a week and have made two quite good no-knead loaves. It seems to be quite active and flavourful. Would the commercial strains have died out by now?