Ah, if only we could answer that, we'd all be rich people!

Sometimes the fares are immediately replaced with identical or near-identical fares, but unadvertised and unpromoted. (I suspect that when this is done, it's to make sure that BA's flights continue to show on multi-airline searches, but when BA does not want to positively encourage low-yield bookings any more.)

Sometimes there will be a lull when the normal fares are in place, and then some sale-level fares come back in. They may or may not be advertised as a sale.

Often, the follow-on sale-level fares (whether or not advertised) are only for a limited selection of destinations, when compared to the wide-ranging promotional sale.

So it's all pot luck, really.

The only thing that one can safely say is that there will be another sale along, at some time. We just don't know when, for how long, or to which destinations. (Neither, to be fair, does BA - they must design these to match what they see as their marketing needs at the time of the sale.)