On cessation by the donor of the property to continue paying a market rent then the reservation of benefit provisions apply. As the property will then be subject to IHT as part of the donor’s death estate if the individual to whom the original gift was made was a lineal descendant the RNRB will be available.
The reference to the date 8.7.15 is of relevance under the downsizing rules under which the property gifted has to have been owned on that date.
If I’m correct it seems somewhat strange that to obtain the RNRB in your case that the donor deliberately triggers the reservation of benefit provisions !!