I think the politics of Russia will collapse or grind to a halt and the most powerful boyar families will compete for the throne either openly or silently.Well, regardless of whether Peter was captured or killed, most of his people saw him as the Antichrist, so they might declare him dead or deposed and raise his son, Alexei, to the throne. And there go all Peter's reforms. Alexei was betrothed but not yet married to Charlotte of Brunswick-Wolfenbuttel, so he may take the chance to break off the betrothal and marry a Russian noblewoman. No idea who exactly.
I think the politics of Russia will collapse or grind to a halt and the most powerful boyar families will compete for the throne either openly or silently.
The boyars or noble class in general will work to undo Peter's work they weren't on his side.