We have "the mind is still present", which gave Jay the impression for years that he wasn't multiple, until he realized it was an impersonal observance mechanism and not himself personally. This is how we remember what goes on and don't "lose time" (actually, lose continuity).

If we had a thing like that happen here, we would think it was glitches in the operating system as new people make themselves known. It doesn't sound like you will lose yourself. The main thing is to work together to be sure you still communicate. If people don't usually break off in your group, Hayden probably didn't -- just because he appeared after Toby felt negative emotions doesn't necessarily mean a split. Maybe you guys became aware of him because of Toby's feelings (maybe he showed up to help?), or maybe he just happened to show up. Or he could have broken off (try asking him?), but if your system doesn't usually work that way, chances are he didn't. Can you keep track through notes or a diary?