They will nominally disappear. PL / NCdot have been in an unofficial coalition since forever, and will continue to draw upon TEST's resurgent manpower when they feel they need it - but only if an existential threat appears / big enough stomp target presents itself. You can expect a six month honeymoon period or so as the MBC helicopter dicks around anything that it feels like burning, but after that your member alliances are probably going to their separate ways.
But I don't think we'll see any major GSF-led coalition arising any time soon (and I genuinely fucking hope there won't be one, coalitions are shit - they subsume small alliance ambitions (which is what builds fun content in EVE) into some retarded concept of ~the greater good~ and everyone suffers as a result).
Hopefully we'll carve out some space in ancestral Delve or Syndicate or somewhere, while the alliance revitalizes and divests itself of the ungodly amount of shitlers we've acquired over the past two years.
EDIT: Just realized that I still have like 40B assets trapped in YA0, welp.