If you're referring to a normal (non-ward) threshold, it won't stick around long. It's not purpose built and doesn't have anything dedicated to extending duration - so it's going to degrade each sunup and sundown (and other time based thresholds such as equinoxes).
Don't think there's anything official on how long it would take, but I'd say most thresholds would be gone by the time the new owner moves in. (Closing on property in the US takes around a month...often more. Also, any house on the market probably had several potential buyers walking through...and degrading the threshold since they aren't family.)
Mechanically, I'd be tempted to allow a Declaration to specify a minor threshold remnant if the buyer has appropriate justification. Without the declaration, there's no remaining threshold.
Welcome by the way!