I can't decide if that pic is an O2 tube or if it's some type of ear 'wire' for communications. But TBF, he was apparently feeling 'fatigue' so it wouldn't be unusual to give O2 to enable him to walk 'in a normal fashion' to Marine One.
Bottom line is, they've never been honest about his health before so they certainly aren't going to start now. The first we know anything will be if there is a formal transfer of power by Scrotus himself since (IIRC my civics re the 25th Amendment) the Speaker of the House and the President Pro Tem of the Senate are notified. And I can't see him EVER voluntarily ceding power to anyone. If the president is suddenly incapacitated I believe the VP & the Cabinet notifies the Speaker and Pres Pro Tem. In either case, the VP then assumes power until such time as POTUS takes it back via letter to Congress.
The 25th Amendment was NOT invoked when Reagan was shot, I suppose because he wasn't 'out of it' long enough to disrupt the govt.
The WH has a fully equipped medical suite that apparently is able to handle just about anything so he should have been able to be treated there. Someone mentioned (don't remember if it was here or on TV) that sending him to WR when he was still ambulatory was to avoid the spectacle of him being wheeled out on a gurney, or worse, red-lighted if his condition were to worsen beyond the WH's medical capabilities.