Should I migrate D7 MLM functionality to D10 or replatform entirely?

Depends on what's working. If your storefront and editorial content are healthy on D7, migrate the Drupal layer to D10 and bridge to a SaaS MLM platform via Pattern B; this is cheaper than a full replatform and preserves the Drupal investment. If everything is fragile, the migration window is the right time to replatform off Drupal entirely. The decision usually turns on the Drupal team: if they're strong and engaged, Drupal stays. If the Drupal investment is more historical than active, the migration window is your cheapest exit.