Further to my earlier reply (hard to type at length on an iPhone...), the timescale for slot transfer is laid down in the document I linked to. Final confirmation by IAG that they are transferring slots to Airline X is due within three weeks of the end of the
IATA slot conference, in other words by early July. If a carrier has applied for some or all of these slots, they will be told before the slot conference whether they are the preferred recipient or not (see section 1.4.11) so they will know whether to plan around these slots or not. I would therefore not expect to hear anything before mid-June (assuming there *is* at least one valid applicant), and I wouldn't expect anything definitive in terms of published flight timings until early July.
And if no one wants to take on the routes ..... ?
Well, then, I imagine IAG doesn't have to give up the slots. The remedies are intended to enable competition on specific routes, not to reduce IAG's overall share of LHR slots.
C.