It surely would be the forest ident if we're speculating about which of the on air set they'll use? Of course they might use something entirely different.
Forest was intended for extreme and sombre situations - so in the case of the Queen dying - it would be suitable on that basis. TWO would either use Silk or Swan for the most part.
Programming schedules would be cleared heavily on the major channels in favour of breaking news coverage and documentaries on the Queen's life; edgy comedy and satire in particular on the BBC would be absent for several days.
With such a situation like this, it also remains to be seen whether ITV, Channel 4 and Channel 5 would also lead their digital offshoots into breaking news, or let through the usual schedule in the wake of the Queen's death.
On the whole, a fascinating and intriguing article. Reading it right now as I speak.
"Winner Winner Chicken Dinner" - PlayerUnknown's Battlegrounds