None VISA holders would be detained in sterile airside accommodation- Pretty standard procedure round the world .
Any lengthy stay might involve a bonded coach and hotel room for those on none VISA holders again pretty normal arrangements for “guests” and at all the Chinese carriers expense.
Contrary to the journalistic narrative and dire political relations we are not at war with Russia (just yet) and subject to individual VISA regulations travel between the domains remains doable from our side . (I’ll caveat that with the current conscription of younger and working class males in Russia )
Airlines continuing to cross Russian airspace include Air India, Emirates, Qatar, Pakistan , El-Al, THY, Fly Dubai and Mongolian all carrying Western Passport holders including US, EU and indeed UKNi citizens without even considering the Chinese carriers !