NISA website. The TLDR is that they would pursue division 2 instead of 3 in this scenario.

“In a scenario where NASL survives, a merger with NISA makes sense. NASL teams would form the core of NISA Division II, while Wilt and team build out NISA Division III from the current pool of applicants that includes investors in Charlotte, Connecticut, Milwaukee, Omaha and St. Louis as well as existing clubs FC Arizona, Chattanooga FC and Miami United FC of the NPSL. Beyond the applicants, NISA already has seven Letters of Intent and is in discussions with as many as two dozen other investor groups. By implementing promotion from Division III to Division II without relegation until Division II hits 20 teams, the NISA model can prevent the problems with having enough teams in the league that have plagued NASL to date. The robust expansion pipeline NISA has developed would be used to backfill Division III until it hits 24 clubs, at which point the work would begin to create the full season Division IV league.”