The following Thursday, the 7.00-7.30 slot on Radio 1 was filled by the last 30 minutes of Jakki Brambles' show - while she was hosting her last TOTP at the same time in NICAM stereo on BBC1.
Yes, although to be a DREADFUL pedant, Pops was on Friday that week because of Hospital Watch at 7pm every night. As you say, when BBC1 went officially stereo, the Radio 1 simulcast ended, although I remember when the revamp happened a few weeks later, there were loads of complaints about it in Smash Hits and someone wrote "Why have Radio 1 stopped broadcasting it? Do they think the new show is crap?"
Although the Beeb officially launched stereo on 31st August 1991, I think they only chose that day because it was when pretty much all the transmitters were in stereo and pretty much all of the programmes were and they'd been broadcasting in stereo for the previous few years. That was different from C4 who promoted their stereo output from the late eighties even though you could only get it from the Crystal Palace and Emley Moor transmitters, and similarly the various ITV regions promoted it when it reached them.
Oddly when they stopped broadcasting Pops on Radio 1, it was replaced by an extra half an hour of Jakki Brambles and they branded that bit as Brambles' Breakers, which does just sound like an audio version of Top of the Pops - https://genome.ch.bbc.co.uk/schedules/radio1/england/1991-11-28#at-18.00.
It always seemed a weird slot, Jakki Brambles' - ninety minutes from Monday to Wednesday and an hour on Thursdays.
Those episodes coming from that very strange short lived era in the lead up to the 1991 revamp where they slightly altered the opening titles by having numbers flying across them, they did the entire 40-2 countdown over a video and they put the presenters out of the way of the audience on gantries and balconies for some reason.
Yes, although it does seem to go in cycles how they do the links - at the moment in 1986 we're not seeing the hosts with the audience much and they do most of the links from empty stages or alone on the gantry. It seems like Stanley Appel wasn't a fan of putting them within the audience very much. But as you say, in that period they were almost always on their own, I remember one episode where Nicky Campbell did most of the links in front of a CSO backdrop (he was in the studio, though). Quite an interesting period, that, a weird transitional phase.