powerful healing magic is only possible by "de-threading archways".
imagine your world lines as strings.
you have to re-trace a significant set of archways (such as walking in a special building's front and back door, or a cave, or tree/hedge),
e.g. if you and your best friend walked through a green building and a red cave in two different towns, you have to walk through them in reverse.
if the building or cave collapses, rebuild it.
friend/clique/family group is heal-able.