As existing French drain for the site is now disconnected where is the water at the disconnected end going? The only way is UP!
This will cause flooding at the surface at its lowest point which could be adjacent to your house.
The new French drain is purely to drain the area within 3m from your house so it complies with NHBC standards. Depending on levels and gradients of your garden you may well still have surface water flooding beyond the 3metre mark which is not covered under the warranty.
As for structural issues, this will be determined by many factors such as type and depth of your foundation, and classification of sub strata and location and species of trees with roots near to you property.
Who is the housebuilder?