If he still hasn't returned in roughly 4 days, and if everybody's cool with it, I'll gently write Ishida off the rooftop and have him leave someone in charge temporarily.

I've been thinking about it and from Ishida's point of view, the best candidate for a temporary boss is probably Tamura, then followed by Umeko, with Takanashi as a distant third.

My theory: Marada's involvement in the gang is too impersonal for Ishida's tastes; he would worry that she's too willing to turn the other members into sacrificial pawns in the event that she's placed in charge of the big picture. Yonaka is decisive and headstrong, but also too foolhardy for sensible decision-making. Toronaga conversely is a little on the uncertain side, hesitating, often until his back is to the wall, to act. A good thinker, though.

Meanwhile Tamura and Umeko strike the best balance of strategy and decisiveness, strength and cunning, courage and collectedness ...

This is only my speculation, though, and of course OOC willingness to play temporary GM takes precedence.